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Polar Y6Pt13X4 (X = Al, Ga) compounds feature Pt-filled Y6 octahedra embedded in the XPt3 framework.

In the frame of this work microporous silicon (mPSi) is filled with magnetic metals (Ni, Co) resulting in a composite system with specific magnetic properties corresponding to its branched morphology. The results are compared with mesoporous silicon (PSi) loaded with Ni nanoparticles (NPs) of comparable size. The two systems offer drastic differences in their magnetic response. Furthermore mPSi offers luminescence in the visible range, whereat this behavior is due to the small structure size in the range of a few nanometers (2 – 5 nm). The morphology of mesoporous silicon shows straight pores with a diameter up to 50 nm. Due to the different template morphology the responding magnetic behavior shows distinct properties related to the two systems, although the size of the metal deposits is in a similar size range. The Ni loaded mPSi system merges optical and magnetic properties leading to a nanocomposite appropriate for possible magneto-optical devices.

Discovered more than 200 years ago in 1821, thermoelectricity is nowadays of global interest as it enables direct interconversion of thermal and electrical energy via the Seebeck/Peltier effect. In their seminal work, Mahan and Sofo mathematically derived the conditions for 'the best thermoelectric'-a delta-distribution-shaped electronic transport function, where charge carriers contribute to transport only in an infinitely narrow energy interval. So far, however, only approximations to this concept were expected to exist in nature. Here, we propose the Anderson transition in a narrow impurity band as a physical realisation of this seemingly unrealisable scenario. An innovative approach of continuous disorder tuning allows us to drive the Anderson transition within a single sample: variable amounts of antisite defects are introduced in a controlled fashion by thermal quenching from high temperatures. Consequently, we obtain a significant enhancement and dramatic change of the thermoelectric properties from p-type to n-type in stoichiometric Fe

Discovered exactly 200 years ago in 1821, thermoelectricity is nowadays of global interest as it allows to directly interconvert thermal and electrical energy via the Seebeck/Peltier effect, which could be exploited to enhance energy efficiency. In their seminal work, Mahan and Sofo mathematically derived the conditions for ’the best thermoelectric’ − a delta-distribution-shaped electronic transport function, where charge carriers contribute to transport only in an infinitely narrow energy interval. So far, however, only approximations to this concept were expected to really exist in nature. Here, we propose as a physical realisation of this scenario the Anderson transition in an impurity band, i.e. the transition from Anderson-localised to extended quantum states. We obtained a significant enhancement and dramatic change of the thermoelectric properties from p-type to n-type in the stoichiometric Heusler compound Fe2VAl, which we assign to a narrow region of delocalised electrons in the energy spectrum near the Fermi energy. We achieved this through an innovative approach of driving the Anderson transition via continuous disorder tuning: variable amounts of atomic defects are induced in a controlled fashion by thermal quenching from high temperatures (950 − 1380 °C). Based on our experimental electronic transport and magnetisation results, supported by Monte-Carlo and density functional theory calculations, we demonstrate a universal enhancement strategy towards colossal thermoelectric performance that is applicable to diverse material classes.

The crystal structure of phases in the pseudo-binary system CeCo1–хNiхC2 (x = 0, 0.33, 0.5, 0.67, 0.79, 0.80, 0.83, 1) was investigated by means of X-ray powder diffraction. Co richer solid solutions CeCo1–хNiхC2 (0≤ x ≤0.5) crystallize in the monoclinic CeCoC2-type structure; a = 5.3968(2) Å, b = 5.4013(3) Å, c = 7.4762(3) Å, β = 102.136(3)°, V = 213.06(3) Å3 for x = 0.5. Ni-rich CeNi1–yCoyC2 (0≤ y ≤0.2) are isotypic with the orthorhombic CeNiC2-type structure, a = 3.8486(2) Å, b = 4.5479(2) Å, c = 6.1531(3) Å, V = 107.70(1) Å3 for y = 0.2. In the intermediate region (0.5< x 0.21Ni0.79C2 and CeCo0.5Ni0.5C2, coexist. The non-isoelectronic substitution of Ni by Co in solid solutions CeNi1–yCoyC2 causes a continuous reduction of the Néel temperature and finally, for CeCoC2, results in a paramagnetic Kondo-lattice ground state.

The isothermal section of the phase diagram of Tb–Fe–C system at 800 °C was studied in the full concentration range using powder X-ray phase and structure analyses, and energy-dispersive X-ray spectroscopy. Six ternary compounds Tb1.88Fe14C, Tb13Fe10C13, TbFeC2, Tb15Fe8C25, Tb5.64Fe2C9, Tb2FeC4 and a limited solid solubility of carbon in the crystal structure of the binary parent compound Tb2Fe17Cх (0≤ х ≤0.8) have been found to exist at 800 °C. The crystal structures of two new ternary carbides have been determined by means of powder X-ray diffraction: Tb15Fe8C25 with structure type Er15Fe8C25, space group P321, a = 11.9706(3) Å, c = 5.1733(2) Å, RB(I) = 0.07, RP = 0.06, RPw = 0.08, and Tb13Fe10C13 with structure type Gd13Fe10C13, space group P3121, a = 9.1800(9) Å, c = 23.703(5) Å, RB(I) = 0.04, RP = 0.16. Both compounds are representatives of the carbometalate class of complex carbides. Tb15Fe8C25 displays an itinerant ferro-or ferrimagnetic ordering of the Fe 3d-moments below TM ≈ 50 K while Tb 4f-moments remain essentially paramagnetic at least down to about 10 K.

With a small gap in the density of states and a substantially semiconducting behavior half Heusler alloys have drawn attention as thermoelectric materials. For this study we have selected Hf-free compounds, Ti0.5Zr0.5NiSn, Ti0.5Zr0.5NiSn (with a densification aid (DA)) and Ti0.5Zr0.5NiSn0.98Sb0.02 as well their parent alloys TiNiSn and ZrNiSn as cheap thermoelectrics. Electrical resistivity, thermal conductivity and specific heat were evaluated below room temperature (4.2–300 K) in order to get insight into the mechanism of transport properties. SEM and TEM investigations as well as DFT (density functional theory) calculations accompany this research. The fine-grained epitaxial microstructure with a large number of dislocations warrants a low thermal conductivity at ultralow values (∼30 mW/cmK at 300 K) at a narrow band gap with a sufficiently high density of states at the Femi level. High order of components mixing strongly affects the stability of the solid solutions by the configuration entropy term, which causes a shrinkage of the miscibility gap. For the electronic density of states (DOS) the split Zr band and impurity Ni band induce a significant reduction of the effective energy gap and thus explain n-type of conductivity of the compounds and solid solutions studied.

The crystallographic and physical properties of the recently discovered filled skutterudite superconductor ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$, synthesized by a high-pressure and -temperature technique, are studied by measuring electrical resistivity, specific heat, and magnetization, and by performing electronic band calculations. X-ray powder diffraction with Rietveld refinement indicates that the lattice parameter of ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ is 8.093(2) \AA{} and that fractional coordinates of the P site are [0, 0.3607(9), 0.1450(9)], which is also confirmed by calculations based on density functional theory. The electrical resistivity indicates a metallic nature of ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$, which is consistent with the density of states at Fermi energy with 7.5 (states/eV)/f.u. deduced from the electronic band calculations. The Sommerfeld coefficient $\ensuremath{\gamma}$ and Einstein temperature $\ensuremath{\theta}{}_{\mathrm{E}}$ of ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ are deduced as $\ensuremath{\gamma}\ensuremath{\sim}26\phantom{\rule{4pt}{0ex}}\mathrm{mJ}/{\mathrm{mol}\phantom{\rule{0.16em}{0ex}}\mathrm{K}}^{2}$ and $\ensuremath{\theta}{}_{\mathrm{E}}\ensuremath{\sim}150$ K, respectively. A larger isotropic atomic displacement parameter ${U}_{\mathrm{eq}}$ of Sr compared to other atomic species as obtained from a Rietveld analysis and a specific heat anomaly around 30 K refers to anharmonic lattice vibrations of Sr in ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$. ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ exhibits two superconducting transitions at ${T}_{\mathrm{c}1}=1.6$ K and ${T}_{\mathrm{c}2}=1.0$ K. Specific-heat data indicate that the observed superconductivity is of bulk nature with approximate volume fractions of $27%$ and $38%$ for superconductivity at ${T}_{\mathrm{c}1}$ and ${T}_{\mathrm{c}2}$, respectively. The electrical resistivity under field and pressure as well as the specific heat under field indicate that ${T}_{\mathrm{c}1}$ is sensitive to the magnetic field and ${T}_{\mathrm{c}2}$ is sensitive to pressure. The results show that ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ is an $s$-wave weakly coupled superconductor with an electron-phonon mass enhancement ${\ensuremath{\lambda}}_{\text{ep}}\ensuremath{\sim}0.47$.

The two La2Pd3Ge5 and Nd2Pd3Ge5 compounds, crystallizing in the oI40-U2Co3Ge5 crystal structure, were targeted for analysis of their chemical bonding and physical properties. The compounds of interest were obtained by arc melting and characterized by differential thermal analysis, scanning electron microscopy, and X-ray diffraction both on powder and on a single crystal (for the La analogue), to ensure the high quality of the samples and accurate crystallographic data. Chemical bonding was studied by analyzing the electronic structure and effective QTAIM charges of La2Pd3Ge5. A significant charge transfer mainly occurs from La to Pd so that Ge species assume tiny negative charges. This result, together with the -(I)COHP analysis, suggests that, in addition to the expected homopolar Ge bonds within zigzag chains, heteropolar interactions between Ge and the surrounding La and Pd occur with multicenter character. Covalent La–Pd interactions increase the complexity of chemical bonding, which could not be adequately described by the simplified, formally obeyed, Zintl–Klemm scheme. Electric resistivity, specific heat, magnetization, and magnetic susceptibility as a function of temperature indicate for both compounds a metallic-like behavior. For Nd2Pd3Ge5, two low-temperature phase transitions are detected, leading to an antiferromagnetic ground state., The chemical bonding and physical properties of the two isotypic R2Pd3Ge5 (R = La and Nd) intermetallics are presented. La2Pd3Ge5 shows polar Ge−Pd/La multicenter interactions in addition to covalent Ge−Ge bonds. The bonding scenario is further complicated by the fact that Pd and La are also covalently interacting. For Nd2Pd3Ge5, an antiferromagnetic ground state is established after a long-range magnetic ordering (at ∼7.5 K) followed by a spin-reorientation transition (at ∼6.2 K).

Semiconductor quantum dots (QDs) are widely used for optical applications and bioimaging. In comparison to organic dyes used for fluorescent labeling, QDs exhibit very high photostability and can be further surface modified. Equipping QDs with magnetic properties (mQDs) makes it possible to combine fluorescence and magnetic resonance imaging analyses. For this purpose, we have prepared water-dispersible and magnetic CdTe/ZnS mQDs, whereby ferrous ions are selectively incorporated in either their cores or their shells. This study aims at understanding the differences in optical, structural, and magnetic properties between these core- and shell-doped mQDs. Field-dependent isothermal magnetic susceptibility measurements show that shell-doped mQDs exhibit paramagnetic and their core-doped equivalents superparamagnetic behavior near room temperature. Shell doping results in about 1.7 times higher photoluminescence quantum yields and 1.4 times higher doping efficiency than core doping. X-ray diffraction pattern...

X-ray single-crystal structure analysis was performed for the novel compound V1.84Fe1.16B2 ≡ (V1-xFex)2FeB2 at x = 0.08 (P4/mbm; a = 0.555931(9) nm, c = 0.306781(5) nm; U3Si2-type). Consequently, structural identity is obvious between (V0.92Fe0.08)2FeB2 and the precipitates V∼2Fe∼1B2 earlier identified in the UGISTAB215XH permanent magnet. Magnetic and 57Fe Mossbauer studies of (V0.92Fe0.08)2FeB2 reveal a magnetically ordered ground state with Tc∼110 K. Mossbauer spectra point towards a ferrimagnetic spin arrangement. Enthalpy of formations (DFT calculations) for (Fe,V), VB, V3B2, and the hypothetical solution V3-xFexB2 (x Calculation of the electron localization function elf yielded a very high value (ϒ ∼0.75) between boron atoms documenting strong covalent bonding. The Young's modulus E (from nano-indentation) for V1.84Fe1.16B2 is 442 GPa. The higher anisotropy in the ternary boride V2FeB2 is concluded from the significantly higher difference between C11 and C33 in V2FeB2 (192.1 GPa) with respect to V3B2 (117.0 GPa).

Investigations of phase relations in the ternary system Ti-Fe-Sb show that the single-phase region of the Heusler phase is significantly shifted from stoichiometric TiFeSb (reported previously in the literature) to the Fe-rich composition TiFe1.33Sb. This compound also exhibits Fe/Ti substitution according to Ti1+xFe1.33-xSb (-0.17 ≤ x ≤ 0.25 at 800 °C). Its stability, crystal symmetry and site preference were established by using X-ray powder techniques and were backed by DFT calculations. The ab initio modeling revealed TiFe1.375Sb to be the most stable composition and established the mechanisms behind Fe/Ti substitution for the region Ti1+xFe1.33-xSb, and of the Fe/Co substitution within the isopleth TiFe1.33Sb-TiCoSb. The calculated residual resistivity of Ti1+xFe1.33-xSb, as well as of the isopleths TiFe1.33Sb-TiCoSb, TiFe0.665Co0.5Sb-TiCoSb0.75Sn0.25 and TiFe0.33Co0.75Sb-TiCoSb0.75Sn0.25, are in a good correlation with the experimental data. From magnetic measurements and 57Fe Mossbauer spectrometry, a paramagnetic behavior down to 4.2 K was observed for TiFe1.33Sb, with a paramagnetic Curie-Weiss temperature of -8 K and an effective moment of 1.11μB per Fe. Thermoelectric (TE) properties were obtained for the four isopleths Ti1+xFe1.33-xSb, TiFe1.33Sb-TiCoSb, TiFe0.665Co0.5Sb-TiCoSb0.75Sn0.25 and TiFe0.29Co0.78Sb-TiCoSb0.75Sn0.25 by measurements of electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (λ) at temperatures from 300 K to 823 K allowing the calculation of the dimensionless figure of merit (ZT). Although p-type Ti1+xFe1.33-xSb indicates a semi-conducting behavior for the Fe rich composition (x = -0.133), the conductivity changes to a metallic type with increasing Ti content. The highest ZT = 0.3 at 800 K was found for the composition TiFe1.33Sb. The TE performance also increases with Fe/Co substitution and reaches ZT = 0.42 for TiCo0.5Fe0.665Sb. No further increase of the TE performance was observed for the Sb/Sn substituted compounds within the sections TiFe0.665Co0.5Sb-TiCoSb0.75Sn0.25 and TiFe0.33Co0.75Sb-TiCoSb0.75Sn0.25. However, ZT-values could be enhanced by about 12% via the optimization of the preparation route (ball-mill conditions and heat treatments).

Investigation of the system Th-Ni-B prompted a novel ternary compound ThNi12B6. X-ray structure analysis of single crystals obtained by the mechanical fragmentation of an as-cast sample revealed a fully ordered CeNi12B6-type structure (space group Cmc21, no. 36; a = 0.95638(1) nm, b = 0.73852(1) nm, c = 1.10195(1) nm; RF2 = 0.0305). Density functional theory (DFT) calculations have been performed comprising heat of formation, electronic band structure and density of states, Fermi surface via Wannier functions, phonon band structure and density of states, phonon and electronic contributions to specific heat and elastic constants Cij. Comparing the parameters evaluated from DFT with the experimental data, an overall satisfactory agreement has been achieved. Measurements of electrical resistivity, magnetic susceptibility and specific heat manifest a Pauli paramagnetic, metallic behaviour for ThNi12B6 without any anomalies, in close match with the isotypic homologue LaNi12B6. Static and dynamic hardness data show rather high values; Young's modulus is in the range of 240 GPa. The Debye temperature, θD = 490 K, gained via elastic constants, is slightly higher than the values extracted from specific heat or electrical resistivity data. A rather low coefficient of thermal expansion, α = 5.5 × 10-6 K-1, was derived from the temperature dependent length change.

Magnetic properties of single crystalline HoCoC 2 and the evolution of magnetic and structural features in a series of polycrystalline solid solutions HoCo 1− x Ni x C 2 ( 0 ⩽ x ⩽ 1 ) are investigated by means of X-ray diffraction, magnetization, magnetic susceptibility and specific heat measurements. The crystal structures of all investigated samples refers to the CeNiC 2 -type structure (space group Amm 2 and Pearson symbol oS8). Non-isoelectronic substitution of Co by Ni causes a non-linear increase of the unit cell volume and especially a non-monotonous variation of the a and c lattice parameters as well as a pronounced reduction of the C–C bond length of carbon dimers. Temperature dependent magnetization and specific heat measurements reveal a crossover from a ferromagnetic for HoCoC 2 with T C = 10.6 (1) K to an antiferromagnetic ground state for HoNiC 2 with T N = 2.78 (6) K and a non-monotonous variation of the magnetic ordering temperature with a minimum at intermediate compositions. Crystalline electric field effects of HoCoC 2 and HoNiC 2 are analysed using combined thermodynamic and magnetic susceptibility data. The electrical resistivity of HoNiC 2 displays a distinct anomaly near room temperature which indicates the formation of a charge density wave (CDW) state as earlier reported for several other rare earth nickel dicarbides.

Two boron rich phases were successfully synthesized by borothermal reduction of Yb oxide under vacuum. For the new boron-poorer phase, the single phase was established at around [B]/[Yb] = 43.3 at 1500 °C ( Pbam space group; YB 50 -type; a = 16.5811(5) A, b = 17.5950(5) A, c = 9.4647(3) A; powder X-ray diffraction; Rietveld refinement). The crystal structure of the boron-richer phase ([B]/[Yb] = 56.7) has been elucidated by single crystal X-ray diffraction ( F m 3 ¯ c space group; YB 66 -type; a = 23.3587(6) A). Powder X-ray diffraction data of the alloy YbB ~70 annealed at 1825 °C yielded, along with the YB 66 -type compound (a = 23.3691(2) A), β - rh B as a secondary phase ( R 3 ¯ m space group, a = 10.9298(3) A, c = 23.875(1) A), for which the solubility of Yb was found to be below 1 at%. The Yb atoms in β - rh B occupy the D and E voids. Both YbB 43.3 (YB 50 -type) and YbB 56.7 (YB 66 -type) feature complicated boron atom frameworks which exhibit shorter B-B separations both within and between boron clusters as compared to those observed for prototype structures.

We have studied structural properties of La 3 Ni 2 B 2 N 3− δ samples with distinctly different values of the superconducting transition temperature by means of powder neutron diffractometry and specific heat measurements. The refinement of lattice site occupations reveals full occupations for all sites in the La 3 Ni 2 B 11 2 N 3 structure with space group I 4/ mmm except for nitrogen site N(2). For samples with T c = 13.0 K and 13.7 K we obtain for the N(2) site distinctly different occupation factors of 0.90 and 0.93, respectively. The latter confirms a direct relation between the nitrogen stoichiometry and the superconducting transition temperature. Based on the analysis of temperature dependent lattice parameters, atomic displacement factors, lattice heat capacity data and ab initio phonon density of states calculations we discuss the thermal expansion and vibrational properties of superconducting La 3 Ni 2 B 2 N 3− δ .

Bi-metal magnetic nanostructures have been deposited within porous silicon (PSi) to influence the magnetic switching behavior of the PSi/metal nanocomposite and further to enhance the energy product of the system compared to single metal nanocomposites. These nanocomposites consisting of two ferromagnetic metals have been achieved by two different routes. On the one hand both metals have been deposited alternatingly out of one solution and on the other hand the two metals have been deposited by using different metal salt solutions alternately. The latter system shows two distinct slopes of the hysteresis due to the different saturation behavior of the two types of deposited metal, whereas the system produced from one electrolyte shows no kink which indicates exchange coupling between the two metals. The comparison of these two types of samples shows that the one offering exchange coupling exhibits nearly a doubled coercivity and remanence.

A novel ternary compound, UMo3B7, has been synthesized by arc melting and annealing at 900 °C. Its crystal structure was determined from X-ray single crystal diffraction data (YMo3B7-type structure, space group Pnma; a = 1.10310(8) nm, b = 0.30995(2) nm, c = 1.2792(1) nm, RF2 = 0.0205). The structure is composed of boron filled trigonal prisms as well as unfilled tetrahedra and tetragonal pyramids formed by metal atoms. With respect to boron atoms aggregation, it exhibits a well-developed two-dimensional boron network revealing infinite bands of edge linked boron hexagons. The relationship with the members of the structural series within the V-B system: VnBn+1 = (n-1)VB (CrB-type) + VB2 (AlB2-type) (n = 1, 2, 3, 5) is discussed. Specific heat, magnetic susceptibility and electrical resistivity measurements characterize UMo3B7 as a spin fluctuating system.

A new member of the series of Th7 Fe3 -type derivative structures, h-(Pd0.86 Cu0.14 )7 B3 (≡Pd6.02 Cu0.98 B3 , unique structure type Pd6 CuB3 , space group P63 cm, a=12.9426(9) A, c=4.8697(4) A, single-crystal X-ray diffraction (XRD) data) was obtained from as cast alloys and alloys annealed at 600-650 °C. Further substitution of Cu by Pd led to formation of a Mn7 C3 -type structure, o-(Pd0.93 Cu0.07 )7 B3 (≡Pd6.51 Cu0.49 B3 , space group Pnma, a=4.8971(2) A, b=7.5353(3) A, c=12.9743(6) A, single-crystal XRD). Isotypic LT h-(Pt0.70 Cu0.30 )7 B3 (≡Pt4.90 Cu2.10 B3 ) was observed in the Pt-Cu-B system as a low-temperature (LT) phase (T≤600 °C) (powder XRD), whereas the Th7 Fe3 -type (high-temperature (HT) h-(Pt0.73 Cu0.27 )7 B3 ≡Pt5.11 Cu1.89 B3 , space group P63 mc, a=7.4671(1) A, c=4.9039(1) A, powder XRD) proved to be stable at high temperature. The three structures are built of columns of face connected metal octahedra and columns of metal tetrahedra alternatingly fused by common faces and vertices. Boron atoms are found in trigonal prisms formed by metal atoms. The volumes of the three new Th7 Fe3 -type derivative borides relate as 1:2:3. Superconductivity was discovered for Pt4.9 Cu2.1 B3 (Pd6 CuB3 -type) and Pt5.1 Cu1.9 B3 (Th7 Fe3 -type) below 0.67 and 0.66 K, respectively. Despite the close value of the transition temperature the values of the upper critical field at 0 K differ as 0.37 T and 0.27 T for the two compounds.

The constitution of the two phase diagrams Nb-Mn and Ta-Mn has been determined from light optical and transmission and scanning electron microscopy (LOM, TEM and SEM) with energy dispersive (EDX) as well as wavelength dispersive (WDX) X-ray spectroscopy, X-ray powder (XPD) and single crystal diffraction (XSCD), differential thermal analysis (DTA) and/or differential scanning calorimetry (DSC). The Laves phases NbMn2 and TaMn2 are the only binary compounds in these systems. High-temperature differential thermal analyses revealed congruent melting for NbMn2 with T,(NbMn2) = 1515 +/- 15 degrees C, whereas TaMn2 melts incongruently with T-m(TaMn2)= 1797 +/- 40 degrees C close to a depleted peritectic reaction. Both Laves phases engage in eutectic reactions l (Mn) + Nb(Ta)Mn-2 (T-eut = 1220 +/- 10 degrees C at 4.9 at% Nb and T-eut = 1234 +/- 10 degrees C at 0.7 at% Ta, respectively). NbMn2 also forms a eutectic with (Nb): l (Nb) + NbMn2 at T-eut = 1493 +/- 15 degrees C and 53.2 at% Nb. Mn shows remarkably large maximum solid solubilities of 19.4 at% Mn in (Nb) as well as of 21.3 at% Mn in (Ta). Detailed atom site distribution has been established for the Laves phases by means of temperature dependent X-ray single crystal data (both C14 - MgZn2-type). Combined data from XPD, EDX/WDX and SEM microstructure indicate that for both Laves phases extended homogeneity regions exist: Nb1+xMn2+x (62.5-73.0 at% Mn at 950 degrees C: -0.19

In the frame of this work microporous silicon (mPSi) is filled with magnetic metals (Ni, Co) resulting in a composite system with specific magnetic properties. The results are compared with mesoporous silicon (PSi) loaded with Ni nanoparticles (NPs) of comparable size. The mPSi offers luminescence in the visible, whereat this behavior is due to the small structure size in the range of a few nanometers (2 – 5 nm) [1]. The morphology of mesoporous silicon shows straight pores with a diameter up to 50 nm. The mPSi samples are fabricated by anodization of a moderately doped p-type silicon wafer in a 10 wt% hydrofluoric acid solution. The challenging metal filling of these pores is carried out under cathodic conditions by pulsed electrodeposition. As electrolytes aqueous NiSO4 and CoSO4 solutions are employed. The microporous silicon offers a branched morphology and thus also the deposited nanosized metal structures are interconnected. The structure size of the porous samples is estimated by photoluminescence measurements to 5 nm which also determines the size of the deposits. Mesoporous silicon is produced by anodization of a highly n-doped silicon wafer resulting in straight pores of about 50 nm in diameter [2]. The loading of these samples with Ni NPs is also performed by electrodeposition. Magnetic filling of meso- and microporous silicon, respectively means a change in the morphology as well as in the structure size of the magnetic precipitations and both influence the magnetic behavior of the composite system drastically. In the case of mPSi also the luminescence is influenced in its intensity and wavelength by the magnetic filling. The magnetic properties are investigated with a Vibrating Sample Magnetometer (VSM) and a SQUID, respectively. A luminescence spectrometer is used to measure the intensity and the peak position of the photoluminescence spectrum. The structure is investigated by SEM and TEM. Field dependent magnetization measurements show a distinct difference between Ni filled mPSi and PSi loaded with Ni NPs. Considering mPSi filled with Ni and Co a strong magnetic anisotropy between the two magnetization directions applying a magnetic field perpendicular and parallel to the surface, respectively is observed, whereas in the case of Co this behavior is even more pronounced. Figure 1 depicts the hysteresis of mPSi and mesoporous silicon filled with Ni. The coercivities do not vary in a broad range between Ni and Co samples but the saturation field differs drastically between the two materials. In contrast mesoporous silicon loaded with Ni NPs offers only a small magnetic anisotropy caused by weak magnetic interactions between the Ni deposits. Since the microporous silicon offers photoluminescence the huge magnetic anisotropy is of interest for magneto-optical applications. Figure 1: Comparison of field dependent magnetization of mPSi and mesoporous silicon filled with Ni. [1] Handbook of Porous Silicon, Ed. L. Canham, Springer Int. Publishing, 2018. [2] P. Granitzer, K. Rumpf, Semiconductor Science and Technology 31, 4004, 2016. Figure 1

Materials which are close to a quantum critical point are rather prone to magnetic instabilities; even small modifications of relevant interaction mechanisms can be responsible for a magnetic phase transition to occur at finite temperatures. In this work it is demonstrated that actually a substitution of Ce by non-magnetic La in Ce3Pd4Si4 drives a magnetic instability, with ordering temperatures as high as 10 K. To trace the evolution of magnetism and the onset of long range magnetic order in Ce3-xLaxPd4Si4, various bulk property measurements were carried out.

A new Pt-doped yttrium boride of the YB 50 family, YB 45−x Pt y , x = 2.12, y = 0.21 (space group Pbam , a = 16.6246 (4) A, b = 17.6453 (4) A, c = 9.4167 (2) A), has been synthesized by arc-melting pure elements and subsequent annealing at 1123 K. A single crystal has been studied in order to assess the Pt-doping effect on the crystal structure. Insertion of Pt in two 4 h interstitial sites of the boron atom framework leads to the transformation of –[B 12 ]–[B 12 ]– icosahedral chain into –[B 11 ]–Pt–[B 11 ]– for 38.6% of them as well as, to a lesser extent, induces disorder into the [B 15 ] polyhedron and neighboring interstitial B site (97.3% vs 2.7%).

Atom order in the crystal structures of Yb2Cu2-xMg (x = 0.17; Mo2FeB2-type; P4/mbm; a = 0.75592(2) nm; c = 0.40282(1) nm) and Yb9+xCuMg4-x (x = 0.034; Hf9Mo4B-type; P63/mmc; a = 1.0169(5) nm; c = 1.0290(5) nm) was determined from powder and X-ray single-crystal counter data analyses supported by electron probe microanalyses. Among the group of the so-called κ-phases, Yb9+xCuMg4-x is the first representative formed by a lanthanoid element. The structure of this κ-phase can be viewed as a typical network of corner-connected empty Yb6-octahedra, which encompass Yb6Mg6-icosahedra (filled by a mix of Mg/Yb atoms) and Yb6-trigonal prisms centered by Cu atoms to complete the three-dimensional metal framework. From another point of view, the same structure is considered as built from infinite polyicosahedral columns of Yb9Mg4 composition with Cu atoms located in trigonal prismatic interstices, highlighting similarities with other Yb-rich Yb-Cu-Mg phases. Density functional theory (DFT) calculations classify Yb9CuMg4 as a polar intermetallic. Metallic-like behavior is inferred from the Sommerfeld constant, γ = 49.2 mJ/mol·K(2), derived from the electronic density of states, calculated at the Fermi level. DFT integration of the f-density of states indicates almost completely filled f-states, revealing 13.6 and 13.7 electrons in the valence band for Yb1 and Yb2 atoms, respectively, close to the Yb(2+) ground state ((1)S0) for both Yb atoms. Magnetic susceptibility data recorded on the same compound are consistent with a nonmagnetic divalent Yb(2+) state. Temperature-dependent heat capacity data display a metallic behavior characterized by a small Sommerfeld constant γ = 64.8 mJ/mol·K(2) and a rather low Debye temperature ΘD = 140 K as typical for soft materials.

Homogeneity ranges and lattice parameters of the ternary compounds RxZr1-xNi2 (R = Gd−Lu) with cubic MgCu2-type structure have been refined from powder XRD and EDXS data: 0.22 ≤ x ≤ 0.27 for Gd, 0.12 ≤ x ≤ 0.27 for Tb and Ho, 0.12 ≤ x ≤ 0.24 for Dy, Er, and Tm, 0.22 ≤ x ≤ 0.24 for Yb and 0.23 ≤ x ≤ 0.24 for Lu at 870 K. The crystal structure has been also investigated for two single crystals Dy0.16Zr0.84Ni2 and Tm0.17Zr0.83Ni2 from the XRD data: MgCu2 type structure, space group Fd 3 ¯ m, Z = 8, a = 6.988(5) A, R1 = 0.055 for 54 independent reflections Io > 2σ(Io)) for Dy0.16Zr0.84Ni2 and a = 6.976(5) A, R1 = 0.053 for 46 independent reflections Io > 2σ(Io) for Tm0.17Zr0.83Ni2. The electronic structure of RxZr1-xNi2 was studied with the TB-LMTO method. Y0.22Zr0.78Ni2 and Lu0.23Zr0.77Ni2 are temperature independent Pauli paramagnets and exhibit for T

Luminescent porous silicon which is denoted as microporous silicon offers a structure size of a few nanometers. It is filled with magnetic metals resulting in a composite system with specific optical and magnetic properties. The morphology of microporous silicon offers a branched network of pores. The luminescence which is observed in the red-orange region due to the small structure size is influenced by the metal filling. The magnetic response of the samples is related to the interconnected pores and differs significantly to mesoporous silicon filled with magnetic nanostructures of similar size. The luminescent porous silicon is etched in aqueous hydrofluoric acid solution by applying a current density of 10 mA/cm2 for 20 min resulting in a porous layer of about 0.8 µm thickness. The metal filling of microporous silicon is a challenging procedure which is carried out under cathodic conditions by pulsed electrodeposition. As electrolytes adequate metal salt solutions are used. The deposited nanosized metal structures are of the same interconnected sponge-like morphology as the template material. Mesoporous silicon offers oriented pores whereas the diameter is in the range of 50 nm [1]. Also in this case the metal nanoparticles are electrodeposited within the matrix material. The magnetic properties of the different systems rely on the morphology of the template material and the size and geometry of the incorporated metal deposits. The magnetic response offers a significant difference between filled luminescent and mesoporous silicon samples. Luminescent metal filled samples show strong magnetic anisotropy between the magnetization parallel and perpendicular to the surface. For these specimens also significant differences of the anisotropy can be observed depending on the kind of deposited metal, e.g. Ni or Co. These differences are not so distinctive in the case of mesoporous metal filled silicon because of weak magnetic interactions between the metal nanoparticles. Due to the merged optical and magnetic properties in the case of microporous silicon the nanocomposite could be promising for integrated magneto-optic devices. [1] P. Granitzer, K. Rumpf, Semiconductor Science and Technology 31, 4004, 2016.

Magnetic ($\chi$), transport ($\rho$) and heat capacity ($C_m$)properties of CeIrSi are investigated to elucidate the effect of geometric frustration in this compound with trillium type structure because, notwithstanding its robust effective moment, $\mu_{\rm eff}\approx 2.46\mu_B$, this Ce-lattice compound does not undergo a magnetic transition. In spite of that it shows broad $C_m(T)/T$ and $\chi(T)$ maxima centered at $T_{max}\approx 1.5$\,K, while a $\rho \propto T^2$ thermal dependence, characteristic of electronic spin coherent fluctuations, is observed below $T_{coh} \approx 2.5$\,K. Magnetic field does not affect significantly the position of the mentioned maxima up to $\approx 1$\,T, though $\chi(T)$ shows an incipient structure that completely vanishes at $\mu_0 H \approx 1$\,T. Concerning the $\rho \propto T^2$ dependence, it is practically not affected by magnetic field up to $\mu_0 H = 9$\,T, with the residual resistivity $\rho_0(H)$ slightly decreasing and $T_{coh}(H)$ increasing. These results are compared with the physical properties observed in other frustrated intermetallic compounds, Comment: 8 pages, 7 figures

Investigation of the system Th-Ni-B prompted a novel ternary compound ThNi

In this paper, we report the transport, thermodynamic, and superconducting properties of a new filled skutterudite ${\mathrm{CaOs}}_{4}{\mathrm{P}}_{12}$ synthesized under high pressure and high temperature. The electrical resistivity of 3.4--4.$8\mathrm{m}\mathrm{\ensuremath{\Omega}}\mathrm{cm}$, carrier concentration of 3.8--6.$1\ifmmode\times\else\texttimes\fi{}\phantom{\rule{4pt}{0ex}}{10}^{20}{\mathrm{cm}}^{\ensuremath{-}3}$, and positive Hall coefficient suggest that ${\mathrm{CaOs}}_{4}{\mathrm{P}}_{12}$ is a semimetal with hole carriers. An anomaly due to low-energy optical modes corresponding to an Einstein temperature of 150 K was observed in the specific heat. Resistivity, dc magnetic susceptibility, and specific heat measurements indicate bulk superconductivity below 2.5 K. The specific heat anomaly at ${T}_{\mathrm{c}},\mathrm{\ensuremath{\Delta}}C/\ensuremath{\gamma}{T}_{\mathrm{c}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}1.4$, is in agreement with the Bardeen-Cooper-Schrieffer (BCS) value of 1.43. The electron-phonon coupling constant ${\ensuremath{\lambda}}_{ep}$ is estimated to be 0.47. ${\mathrm{CaOs}}_{4}{\mathrm{P}}_{12}$ is classified as a BCS-type, weakly coupled type-II superconductor with an upper critical field of ${H}_{\mathrm{c}2}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}22$ kOe and Ginzburg-Landau coherence length of $\ensuremath{\xi}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}12$ nm.

By combining theoretical density functional theory (DFT) and experimental studies, structural and magnetic phase stabilities and electronic structural, elastic, and vibrational properties of the Laves-phase compound ${\mathrm{NbMn}}_{2}$ have been investigated for the C14, C15, and C36 crystal structures. At low temperatures C14 is the ground-state structure, with ferromagnetic and antiferromagnetic orderings being degenerate in energy. The degenerate spin configurations result in a rather large electronic density of states at Fermi energy for all magnetic cases, even for the spin-polarized DFT calculations. Based on the DFT-derived phonon dispersions and densities of states, temperature-dependent free energies were derived for the ferromagnetic and antiferromagnetic C14 phase, demonstrating that the spin-configuration degeneracy possibly exists up to finite temperatures. The heat of formation ${\mathrm{\ensuremath{\Delta}}}_{298}{H}^{0}=\ensuremath{-}45.05\ifmmode\pm\else\textpm\fi{}3.64\phantom{\rule{0.16em}{0ex}}\mathrm{kJ}\phantom{\rule{0.16em}{0ex}}{(\mathrm{mol}\phantom{\rule{0.16em}{0ex}}\mathrm{f}.\mathrm{u}.\phantom{\rule{0.16em}{0ex}}{\mathrm{NbMn}}_{2})}^{\ensuremath{-}1}$ was extracted from drop isoperibolic calorimetry in a Ni bath. The DFT-derived enthalpy of formation of ${\mathrm{NbMn}}_{2}$ is in good agreement with the calorimetric measurements. Second-order elastic constants for ${\mathrm{NbMn}}_{2}$ as well as for related compounds were calculated.

Metal deposition within porous silicon is under investigation for more than 2 decades whereat the incorporation of metals has been examined with respect to the influence of the light emission or to the modification of the conductivity of porous silicon but also to the growth of different metals inside macropores has been studied in detail. In the frame of this work the deposition of different metals, especially ferromagnetic ones within high aspect ratio mesopores will be elucidated with respect to the specific nucleation and growth of the deposited nanostructures under various conditions. To ensure that the nanostructure growth starts at the pore bottom pulsed electrodeposition has been used. Since mesoporous morphologies offer dendritic pore walls these structural inhomogeneities of the matrices are critical for the deposition process. From experiments one can see that the nucleation preferentially starts at the “tops” of the rough surface. The electrochemical parameters offer the opportunity, but have to be chosen exactly, to obtain desired results. A further key point of the presentation is the magnetic characterization of the various nanocomposites. Magnetic characterization of the three dimensional nanowire/nanoparticle arrays shows that not only the morphology of the deposited metal structures (size, shape, distribution) determines the magnetic properties but also the morphology of the template, e.g. side-pores of different length. In this sense magnetic coupling between the nanostructures plays a crucial role and is strongly influenced by morphological parameters. From all these findings it is possible to prepare samples with specific magnetic properties which could be of interest for on-the-chip devices.

New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt{sub 1−x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.33) forms a B-filled β-Mn-type structure (space group P4{sub 1}32; a=0.6671(1) nm). Cu atoms are distributed preferentially on the 8c atom sites, whereas the 12d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β-Mn-type structure. Pt{sub 9}Cu{sub 3}B{sub 5} (space group P-62m; a=0.9048(3) nm, c=0.2908(1) nm) adopts the Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt{sub 6}] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt{sub 6}] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt{sub 6}] and [Pt{sub 6}] trigonal prisms, rotated perpendicularly to the central one. There is no B–B contact as well as Cu–B contact in the structure. The relationships of Pt{sub 9}Cu{sub 3}B{submore » 5} structure with the structure of Ti{sub 1+x}Os{sub 2−x}RuB{sub 2} as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.3) (B-filled β-Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ{sub 0}H{sub C2}(0){sup WHH} of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt{sub 9}Cu{sub 3}B{sub 5} (Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure) from electrical resistivity measurements. - Highlights: • First two copper platinum borides, (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B{sub 5} were obtained. • (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B forms a B-filled β-Mn-type structure. • Pt{sub 9}Cu{sub 3}B{sub 5} adopts a Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure. • Boron atoms exhibit octahedral and trigonal prismatic coordination. • (Pt{sub 1–x}Cu{sub x})3Cu{sub 2}B (x=0.3) is a bulk superconductor with T{sub c} 2.06 K.« less

The crystal structure, magnetic and electrical transport properties of the new ternary compound Dy 2 Mn 2− x C 5 ( x =0.6) have been investigated. According to X-ray powder diffraction the carbide crystallizes in its own structure type, space group I 4/ mmm , a =3.6421(2), c =15.7713(9) A, R B =0.062, R p =0.134. The crystal structure contains isolated carbon atoms and C 2 dimers in square-bipyramidal holes and distorted bicapped square anti-prisms, respectively. Manganese atomic positions in the structure were found to be not fully occupied. Physical properties were studied in the temperature range down to 0.4 K. The electrical resistivity of Dy 2 Mn 2− x C 5 ( x =0.6) reveals its basically metallic nature with a positive temperature coefficient above about 30 K. A resistive anomaly at around 20 K indicates the appearance of an antiferromagnetic superzone boundary gap at low temperatures. A phase transition towards long range antiferromagnetic magnetic ordering below 19 K is further revealed by heat capacity and ac susceptibility data. Magnetization data refer to a non-trivial nature of the magnetic ground state which may be caused by the intrinsic structural disorder associated with random vacancies at the Mn site.

In the frame of this work porous silicon templates with different morphologies, especially with respect to the roughness of the pore-walls are filled with diverse ferromagnetic metals to fabricate self-assembled three dimensional arrays of nanostructures (wires, particles) with distinct magnetic properties. The fabricated templates offer a quasi-regular self-assembled pore-arrangement with oriented pores. Also the pore-filling is self-assembled by electrochemical deposition and there are multiple possibilities to tailor the magnetic behavior of these systems such as material, morphology, inter particle distance or interfaces. One critical parameter for this purpose is the roughness of the pore walls and the surface of the metal structures, respectively. To vary the morphology of the templates also magnetic field assisted etching has been employed and a remarkable decrease of the dendritic pore growth has been achieved resulting in smoother pore walls. Within the pores of these templates ferromagnetic metals are deposited and the modification of the magnetic properties compared to metal structures embedded in conventional etched (without magnetic field) porous silicon templates has been figured out. The magnetic anisotropy between easy axis and hard axis magnetization could be increased significantly and furthermore the magnetic behavior becomes comparatively hard magnetic. These properties can be ascribed to less magnetic coupling between nanostructures of adjacent pores and modified stray fields due to less dendritic metal nanowires. The magnetic behavior of three dimensional metal nanowire/nanoparticle arrays with regard to morphological parameters as well as to the influence of the inner interfaces of the composites will be presented. The presented system is of interest due to the silicon base material and the broad tunability of the magnetic properties for integrated magnetic and magnetooptic devices.

The crystal structure of the solid solution of DyCo1−хNiхC2 (0≤x≤1) was investigated by means of X-ray powder diffraction: structure type CeNiC2, space group Amm2, and Pearson symbol oS8. The structural analysis reveals a non-monotonous evolution in particular for the a- and c-lattice constants resulting in a non-linear increase of the unit cell volume due to non-isoelectronic substitution of Co by Ni markedly deviating from Vegard׳s law. A crossover from ferro- to antiferromagnetic ordering with a significant reduction of the magnetic ordering temperature at intermediate compositions in DyCo1−хNiхC2 is observed when varying the Ni-concentration. A crossover from ferro- to antiferromagnetic coupling is also revealed from a sign change of the paramagnetic Curie temperature when proceeding along this solid solution.

The novel compounds Ba5{V,Nb}12Sb19+x, initially found in diffusion zone experiments between Ba-filled skutterudite Ba0.3Co4Sb12 and group V transition metals (V,Nb,Ta), were synthesized via solid state reaction and were characterized by means of X-ray (single crystal and powder) diffraction, electron probe microanalysis (EPMA), and physical (transport and mechanical) properties measurements. Ba5V12Sb19.41 (a = 1.21230(1) nm, space group P4[combining overline]3m; RF(2) = 0.0189) and Ba5Nb12Sb19.14 (a = 1.24979(2) nm, space group P4[combining overline]3m; RF(2) = 0.0219) are the first representatives of the Ba5Ti12Sb19+x-type, however, in contrast to the aristotype, the structure of Ba5V12Sb19.41 shows additional atom disorder. Temperature dependent ADPs and specific heat of Ba5V12Sb19.41 confirmed the rattling behaviour of Ba1,2 and Sb7 atoms within the framework built by V and Sb atoms. Electrical resistivity of both compounds show an upturn at low temperature, and a change from p- to n-type conductivity above 300 K in Ba4.9Nb12Sb19.4. As expected from the complex crystal structure and the presence of defects and disorder, the thermal conductivity is suppressed and lattice thermal conductivity of ∼0.43 W m(-1) K(-1) is near values typical for amorphous systems. Vicker's hardness of (3.8 ± 0.1) GPa (vanadium compound) and (3.5 ± 0.2) GPa (niobium compound) are comparable to Sb-based filled skutterudites. However, the Young's moduli measured by nanoindentation for these compounds EI(Ba4.9V12Sb19.0) = (85 ± 2) GPa and EI(Ba4.9Nb12Sb19.4) = (79 ± 5) GPa are significantly smaller than those of skutterudites, which range from about 130 to 145 GPa.

Bi-metal magnetic nanostructures have been deposited within porous silicon to influence the magnetic switching behavior of the porous silicon/metal nanocomposite. These magnetic nanocomposites consisting of two ferromagnetic metals have been achieved by two different routes. On the one hand both metals have been deposited alternatingly out of one solution by changing the potential and on the other hand the two metals have been deposited by using different metal salt solutions. The latter system shows two distinct slopes of the hysteresis curves due to the different saturation behavior of the two types of deposited metal, whereas the system produced from one electrolyte shows no kink which indicates exchange coupling between the two metals. By tuning the amount of each metal the energy product of the systems can be controlled.

Due to the fact that both materials porous silicon as well as iron oxide nanoparticles are biocompatible and porous silicon can be functionalized easily to attach therapeutic nucleotides the aim is to create a cytocompatible arrangement to promote magnetically guided delivery into targeted cells. Furthermore porous silicon dissolves in body fluid dependent on the porosity which increases the possible applications. Within the frame of this work the field and temperature dependent magnetic properties of the nanocomposite have been investigated as well as its cytocompatibility according to the porous silicon morphology and the iron oxide particle size.

Porous silicon in the mesoporous regime is used as template for electrodeposition of ferromagnetic metals within the pores to fabricate self-assembled three dimensional arrays of nanotubes, nanowires or nanoparticles. Depending on the electrochemical deposition parameters the geometry of the metal deposits can be tuned and thus desired magnetic properties can be achieved. The morphology of the templates is modified due to different anodization processes. Additional to a conventional etching process magnetic field assisted etching is applied. Furthermore the magnetic properties in dependence on the morphological characteristics, especially the pore-growth of the porous silicon are investigated. An important point is the concomitant modification of the magnetic coupling of metal nanostructures of adjacent pores.

We report on the formation, physical-chemical, as well as elastic and mechanical properties of the novel Half-Heusler (HH) compound TaFeSb that forms during a solid-state reaction from TaSb2 and TaFe2 in the temperature range between 800 and 850 °C. TaFeSb behaves as a semiconductor, and changes the conductivity type either on temperature or composition. Transport properties of TaFeSb and Ta1-xTixFeSb (0 ≤ x ≤ 0.11) were measured in the temperature range from 4.2 to 823 K, and the effect of titanium on thermoelectric and mechanical properties of Ta1-xTixFeSb was investigated. The Ta/Ti substitution results in a significant increase of the thermoelectric power factor to exciting values of above 6 mW/m⋅K2. In combination with a suppressed phonon thermal conductivity, due to a unique role of Ti, an enhanced figure of merit, ZT900K =1.0 (for Ta0.94Ti0.06FeSb) is obtained, close to the highest values reported for Hf-free p-type HH-systems. In addition, experimental results obtained in this study are discussed and analyzed in the context of ab-initio Density Functional Theory (DFT) calculations.

This work presents the investigation of the magnetic behavior of bi-metal nanostructures within nanostructured silicon with the aim to exploit the magnetic properties of both metals and gain control of the exchange coupling between the two metals especially with respect to their volume ratio. Furthermore a variation of the structure size and the proximity of the metal deposits modify the exchange coupling and thus the energy product. Finally nanocomposite systems with an energy product as high as possible should be achieved to give rise to on-chip applications using permanent nanomagnets, especially arranged in arrays. Magnetic nanostructures of two different metals are deposited within nanostructured silicon to control the magnetic switching behavior of the silicon/metal nanocomposite. Two different templates, porous silicon and porous silicon nanotubes are utilized to achieve such nanocomposites. The morphology (pore diameter, tube diameter) of the two systems is comparable. In the case of the utilization of porous silicon templates a mesoporous morphology with average pore diameters of 50 nm is used and these oriented and separated pores are filled with two different metals, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes. The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer, after the growth of Co particles inside the tubes, as a spacer before the Ni deposition. The morphology of the deposited bi-metal Ni/Co structures is figured out by SEM and EDX, magnetic measurements are performed by SQUID magnetometry. In the presented work the dependence of the magnetic properties of a nanostructured silicon/bi-metal nanocomposite on the volume ratio of the metals, on the proximity of the nanostructures and also on the size of the metal deposits is figured out. If the distance between the deposited bi-metal structures is small enough magnetic exchange coupling between them [1] is present which can be explained by the obtained magnetic data. By tuning the bi-metal deposition an optimized energy product [2] is achieved which gives rise to self-assembled nanocomposite systems containing permanent nanomagnets and arrays of them, respectively for on-chip applications. [1] R. Skomski, J.M.D. Coey, Permanent Magnetism, 1st Edition, CRC Press, Taylor and Francis Group, 1999. [2] R. Skomski, P. Manchanda, P.Kumar, B. Balamurugan, A. Kashyap, D.J. Sellmyer, IEEE Trans. Mag. 49, 3215, (2013).

Constitution of the ternary systems Nb-Co-B and Ta-Co-B was studied, employing optical and electron microscopy, x-ray powder, single crystal diffraction, electron probe microanalysis, DTA and Pirani melting point measurements. Ternary phase equilibria were determined within an isothermal section at 1100 °C. For the Co-rich part (≥50 at.% Co) of the system, a liquidus surface projection and a corresponding Schulz-Scheil reaction scheme were constructed in combination with data for primary crystallization from as-cast samples determined by SEM and EPMA measurements. The crystal structures of novel ternary compounds have been elucidated by x-ray powder and single crystal diffraction and were supported by TEM. {Nb,Ta}CoB with NbCoB-type exhibits a high temperature modification (ZrAlNi-type, a = 0.5953 nm, c = 0.3248 nm; a = 0.5926 nm, c = 0.3247 nm for Nb and Ta respectively), which was only present in as-cast alloys, but found to be stabilized by the addition of Fe to annealing temperatures of 1400 °C. Ta3Co4B7 (a = 0.3189 nm, b = 1.8333 nm, c = 0.8881 nm) was proven to be isotypic with Nb3Co4B7. The novel orthorhombic compounds {Nb,Ta}Co2B3 (TaCo2B3-type with space group Pnma; a = 0.53628 nm, b = 0.32408 nm, c = 1.24121 nm for TaCo2B3; a = 0.53713 nm, b = 0.32442 nm, c = 1.2415 nm for NbCo2B3) adopt unique structure types with branched boron zig-zag chains. {Nb,Ta}Co2B were found to crystallize in a unique monoclinic structure type (space group P21/c; a = 0.9190 nm, b = 0.64263 nm, c = 0.63144 nm; β = 109.954°, for Nb) very close to an orthorhombic setting (Cmce, a = 0.63162 nm, b = 1.72810 nm, c = 0.64270 nm, for Nb). Substitution of Co by Ni stabilizes a smaller orthorhombic lattice with Re3B-type structure (Cmcm) although no homologue compound in the Ni-system exists. The crystallographic relations among the structure types of Re3B and pseudo-orthorhombic as well as monoclinic {Nb,Ta}Co2B were defined in terms of a Barnighausen scheme. DFT calculations revealed very close stabilities for the three competing structure types for {Nb,Ta}Co2B. Detailed transmission electron microscopy (TEM) for Nb(Co,Fe)B, {Nb,Ta}Co2B, {Nb,Ta}(Co,Ni)2B, and Ta3Co4B7 confirmed lattice geometries and crystal symmetry. Vickers hardness was measured for {Nb,Ta}Co2B, {Nb,Ta}(Co,Ni)2B, {Nb,Ta}2−xCo21+xB6 and {Nb,Ta}Co2B3 exhibiting the highest value of hardness of HV = 22.4 ± 1.1 GPa for TaCo2B3. Magnetic, specific heat and electrical resistivity measurements on the compounds TaCo2B and Ta2Co21B6 reveal paramagnetic and ferromagnetic metallic ground states, respectively.

Two novel compounds, EuRh3Ge7 and EuIr3Ge7, have been synthesized by arc melting of the elements and subsequent annealing at 800 °C. X-ray structure analyses confirmed for both compounds isotypism with the crystal structure of the ScRh3Si7-type ( R 3 ¯ c ) : SC-data for EuRh3Ge7 (a = 0.78918(2), c = 2.07179(5) nm, RF = 0.0130) and Rietveld powder data for EuIr3Ge7 (a = 0.788399(5), c = 2.07583 (2) nm, RF = 0.0501). Magnetization, heat capacity, thermal expansion and electrical resistivity at various magnetic fields were measured revealing second order phase transitions at 20 K for EuRh3Ge7, and 87 K for EuIr3Ge7, respectively. While this transition is clearly antiferromagnetic in the case of EuRh3Ge7, the nature of this transition remains unclear for EuIr3Ge7. The evaluation of magnetic susceptibility as well as heat capacity data reveals an intermediate valence state of Eu-ions in both compounds.

Phase relations were investigated for the In-Co-Sb system in the temperature range from 375°C to 800°C using as-cast and annealed alloys. Phase equilibria in the CoSb-InSb-(Sb) composition triangle are presented by a series of isothermal sections and solidus and liquidus surfaces, accompanied by a Schulz–Scheil reaction scheme. The indium-filled skutterudite InyCo4Sb12 already forms an equilibrium with liquid at 484°C, which might limit high-temperature applications of In-Co-Sb-based skutterudites. The maximal solubility of indium in InyCo4Sb12 (y = 0.22) remains almost constant in the temperature range from 475°C to 700°C and corresponds to the equilibrium with CoSb2 and InSb. The solubility of indium in the skutterudite phase is reduced to y = 0.09 when it coexists in equilibrium with InSb and (Sb), and this decrease of the solubility might be responsible for the formation of InSb precipitates. Temperature-dependent x-ray single-crystal and specific heat data for InyCo4Sb12 were employed to determine the rattling behavior of In atoms in the skutterudite lattice.

Ni5P4 crystallizes in hexagonal symmetry, space group P63mc, and adopts its own non-centrosymmetric structure type with lattice constants a=6.78982(4), c=10.98679(7) A according to x-ray powder diffraction. Calorimetric, magnetic and transport studies of Ni5P4 reveal a Pauli-paramagnetic, normal metallic behavior down to 380 mK. The experimental value of the electronic Sommerfeld coefficient γ=13.2 mJ/(mol K2) as well as ab initio electronic structure calculations indicate a moderate electronic density of states at the Fermi level situated near the upper edge of essentially filled d-bands.