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Magnesium silicide (Mg2Si) is a promising eco-friendly thermoelectric material, which has been extensively studied in recent times. However, its phase behavior at high pressures and temperatures remains unclear. To this end, in this study, in situ X-ray diffraction analysis was conducted at high pressures ranging from 0 to 11.3 GPa and high temperatures ranging from 296 to 1524 K, followed by quenching. The antifluorite-phase Mg2Si decomposed to Mg9Si5 and Mg at pressures above 3 GPa and temperatures above 970 K. The antifluorite-phase Mg2Si underwent a structural phase transition to yield a high-pressure room-temperature (HPRT) phase at pressures above 10.5 GPa and at room temperature. This HPRT phase also decomposed to Mg9Si5 and Mg when heated at ∼11 GPa. When 5Mg2Si decomposed to Mg9Si5 and Mg, the volume reduced by ∼6%. Mg9Si5 synthesized at high pressures and high temperatures was quenchable under ambient conditions. Thermoelectric property measurements of Mg9Si5 at temperatures ranging from 10 to 390 K revealed that it was a p-type semiconductor having a dimensionless thermoelectric figure of merit (ZT) of 3.4 × 10-4 at 283 K.

High-pressure techniques open exploration of functional materials in broad research fields. An established diamond anvil cell with a boron-doped diamond heater and transport measurement terminals has performed the high-pressure synthesis of a cubic Sn

High-pressure techniques open exploration of functional materials in broad research fields. An established diamond anvil cell with a boron-doped diamond heater and transport measurement terminals has performed the high-pressure synthesis of a cubic Sn$_{3}$S$_{4}$ superconductor. X-ray diffraction and Raman spectroscopy reveal that the Sn$_{3}$S$_{4}$ phase is stable in the pressure range of P>5 GPa in a decompression process. Transport measurement terminals in the diamond anvil cell detect a metallic nature and superconductivity in the synthesized Sn$_{3}$S$_{4}$ with a maximum onset transition temperature of 13.3 K at 5.6 GPa. The observed pressure-T$_{c}$ relationship is consistent with that from the first-principles calculation. The observation of superconductivity in Sn$_{3}$S$_{4}$ opens further materials exploration under high temperature and pressure conditions.

The effect of temperature on the crystal structure of BaSi 2 was investigated by single crystal X-ray diffraction studies at temperatures ranging from 120 to 300 K. Upon reducing the temperature from 300 to 120 K, the unit-cell volume decreased by ∼1%, while the volume of the Si 4 tetrahedra remained unchanged. First principles calculations revealed that the Si atoms form covalent bonds with three adjacent Si atoms in the Si 4 tetrahedra. These covalent bonds are speculated to be responsible for the constant volume of Si 4 upon cooling.

First-principles calculations of the density of states (DOS) and partial charge distributions for BaSi2 revealed that the electronic states of the valence bands of BaSi2 are mainly derived from the Si 3p states of Si4 tetrahedra formed in BaSi2, while those of the conduction bands originate from the Si 3p states of Si4 and 5d states of the Ba atom. Thus, the molecular orbital diagram of BaSi2 was constructed. The origin of the large slopes at the band edges in the DOS of BaSi2, which results in a high optical absorption coefficient for the material, was discussed.

The synthesis of H−-encaged 12CaO·7Al2O3 (C12A7) crystals was examined by solid-state reactions in a reducing atmosphere using a high-pressure apparatus. Powder X-ray diffraction patterns reveal that the C12A7 crystals are synthesized directly from the raw materials. The synthesized samples show ultraviolet-light-induced coloration, attributed to two absorption bands in the infrared and visible spectral regions, which is consistent with the unique properties of H−-encaged C12A7. The H− concentration is estimated to be ∼0.6 × 1021 cm−3 from the optical absorption spectra. Our results demonstrate that the direct synthesis methods involving solid-state reactions in a reduced atmosphere using a high-pressure apparatus provide an appealing route to obtain C12A7-derived materials with novel physical and chemical properties.

The volumetric thermal expansion coefficient α V is discussed in relation to the bulk modulus B 0 for transition-metal disilicides (TrSi2), alkaline-Earth metal disilicides (AeSi2), Mg2Si, and Si clathrates. For this purpose, the α V of CoSi2 at 300 K is determined to be 3.1 × 10−5 K−1 using powder X-ray diffraction measurements at temperatures ranging from 300 to 835 K. AeSi2 and Mg2Si have B 0 values ranging from 27.9 to 52.9 GPa, while the values for α V range from 3.2 × 10−5 to 4.8 × 10−5 K−1. TrSi2 including CoSi2 has larger B 0 values ranging from 148.9 to 243 GPa and smaller α V values ranging from 2.3 × 10−5 to 3.3 × 10−5 K−1 than AeSi2. Si clathrates have intermediate values of α V and B 0, which are in between those of TrSi2 and AeSi2. Thus, the silicides with small B 0 values tend to have large α V values.

Magnesium silicide (Mg

We report resistance and elastoresistance measurements on $({\mathrm{Ba}}_{0.5}{\mathrm{K}}_{0.5}){\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$, ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, and ${\mathrm{KCa}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{\mathrm{F}}_{2}$. The Fe-site symmetry is ${D}_{2d}$ in the first compound but ${C}_{2v}$ in the latter two, which lifts the degeneracy of the Fe ${d}_{xz}$ and ${d}_{yz}$ orbitals. The temperature dependence of the resistance and elastoresistance is similar between the three compounds. Especially, the [110] elastoresistance is enhanced with decreasing temperature irrespective of the Fe-site symmetry. This appears to be in conflict with recent Raman scattering studies on ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, which suggest the absence of nematic fluctuations. We consider possible ways of reconciliation and suggest that the present result is important in elucidating the origin of in-plane resistivity anisotropy in iron-based superconductors.

In the present advanced information society, the group IV element Si is inevitably used for various high-performance devices, such as transistors and solar cells. When Si meets group-II elements such as Mg, Ca, Sr, or Ba, semiconducting silicides are formed, which are applicable to energy conversion devices such as thin-film solar cells and thermoelectric devices. In this Tutorial, we focus on two representative typical semiconducting silicides among them: Mg2Si and BaSi2 composed of earth-abundant elements. Mg2Si has been extensively studied for light-weight high-performance thermoelectric devices, whereas BaSi2 has been studied for thin-film solar cells, and recently has also been attracting attention as a thermoelectric material. However, these group-II elements are highly reactive with oxygen and water. Thus, we need to be careful when handling these elements. In this Tutorial, we provide guidance on how to handle these group-II elements and their compounds in an easy-to-understand manner for beginners. In addition, we introduce thin-film growth and bulk growth techniques, as well as the points to be considered when characterizing these materials.

The effects of Sr substitution in BaSi2, a promising photoabsorber for thin-film solar cells, were examined computationally and experimentally. The calculations showed that Ba0.5Sr0.5Si2 with Sr atoms at the A1 site (A1-Sr-BSS) is more stable than that with Sr atoms at the A2 site (A2-Sr-BSS). Both materials are indirect bandgap semiconductors. The indirect and direct bandgaps of A1-Sr-BSS are larger than those of BaSi2, while those of A2-Sr-BSS are smaller. The indirect bandgap of A1-Sr-BSS is 0.01 eV higher than that of BaSi2, while that of A2-Sr-BSS is 0.06 eV lower. This trend is attributable to the difference in the electronic properties around the conduction band minimum, which is determined by the type of atoms (Ba or Sr) that occupy the A1 site. Single-crystal X-ray diffraction and diffuse reflectance measurements of Ba1-xSrxSi2 (0.0 ≤ x ≤ 0.8) revealed that the Ba atoms at the crystallographic site A1 are preferentially substituted by Sr atoms and that the bandgap, Eg, decreases with x (1.24 eV at x = 0 and 1.15 eV at x = 0.65). The preferential occupation of the A1 site by Sr atoms is consistent with the computational result that A1-Sr-BSS is more stable than A2-Sr-BSS. However, the experimentally observed decrease in Eg with x is closer to the decrease of −0.06 eV in the indirect bandgap of A2-Sr-BSS than to the 0.01 eV increase in the case of A1-Sr-BSS. The reason for this discrepancy is discussed.

The electronic structure and optical properties of NaSi were investigated using first-principles calculations and diffuse reflectance measurements. The calculation indicates that NaSi is an indirect band gap semiconductor whose valence band maxima and conduction band minima are located at a k-point between the Γ and X points and at the Y point, respectively. NaSi has several direct band gaps, which are approximately 0.1 eV larger than the indirect band gap, leading to its large optical absorption coefficient near the indirect band gap. The valence bands originate from Si-3p states and the conduction bands from the Si-3s, Si-3p, Na-3s, and Na-3p states. Diffuse reflectance measurements revealed that NaSi has a band gap of 1.63 eV, which is comparable to the band gap calculated using HSE06 (1.68 eV).

The effects of substituting Ga atoms with Al on the thermoelectric properties of the ternary Si clathrate K8Ga8Si38 were assessed over the temperature range of 10–700 K. For this purpose, the series of quaternary Si clathrates K8-δGaxAlySi46-x-y (x + y ≈ 8; 0 ≤ y

Barium disilicide (BaSi2), composed of abundant and inexpensive elements, is a potential absorber material for thin-film solar cells. In this study, density-functional theory calculations show that BaSi2 belongs to a Zintl phase with a mixed character of covalent units of tetrahedral Si4 with an ionic nature described by (2Ba2+)(Si4)4−. The molecular orbital diagram is elucidated based on the electronic structures, suggesting that the charge transfer transition from Si p to Ba d greatly enhances optical absorption. A large photoabsorption coefficient is confirmed using advanced excited state calculations that include excitonic effects. The ionization potential of BaSi2 is smaller than that of silicon or germanium, suggesting that the band edge positions are suitable for p-type conductivity and type II heterojunctions for BaSi2/Si or BaSi2/Ge. The chemical potential window for the stable growth of a stoichiometric BaSi2 film is very narrow, and the stability of native defects is investigated under realistic growth conditions. Si vacancy, Ba substituted for Si antisite, and Si interstitial defects are predominant but do not cause the generation of a significant number of carriers. The calculated Fermi level is pinned in the middle of the band gap for the entire silicon chemical potential range and a wide growth temperature range, indicating the feasibility of bipolar doping, which is advantageous for fabricating p–n junctions.

Thin films of guest-free type-II Si clathrate (Si136) were fabricated on Si(111) wafers in two steps: NaxSi136 thin-film formation by thermal decomposition of NaSi precursor films and Na removal from the NaxSi136 film by a heat treatment with iodine. Cross-sectional TEM observation and XRD and Raman measurements verified the formation of 1-μm-thick Si136 films on the Si wafer. Since the prepared films showed n-type conduction, pn junction devices were developed by a Si136/p-type Si structure. This device showed a photovoltaic (PV) response under white light illumination. The thin film formation and the PV response of Si136 indicated this Si allotrope to be the next-generation platform for semiconductor technology.

Thermoelectric power generation in the low temperature region has attracted considerable attention as a means of the effective use of distributed energy and for sensor applications. However, it is difficult to theoretically predict the exact thermoelectric transport properties owing to the relatively narrow bandgap of low temperature thermoelectric materials. In this study, a high-purity α-SrSi2 crystal was synthesized by the vertical Bridgman (VB) method. The carrier density of the VB-grown α-SrSi2 was investigated, and, from the temperature dependence of the carrier density, it was estimated that the bandgap was 13.1 meV. First-principles calculations using the Heyd–Scuseria–Ernzerhof screened hybrid functional for α-SrSi2 predicted the bandgap to be very close to this value (13.27 meV) when assuming the mixing parameter of the Hartree–Fock contribution to the exact exchange is 18.7%. Using the calculated electronic structure and the measured carrier concentration, the predicted temperature dependence of the Seebeck coefficient was in good agreement with the experimental results.

In the interest of the sustainable development of society, it is preferable to construct next-generation thermoelectric devices using materials from earth-abundant elements. In conventional thermoelectric devices for low temperature applications, Bi2Te3-based materials that consists of scarce elements have been used. Cubic strontium disilicide (SrSi2) is a potential thermoelectric material for low temperature applications that consists of earth-abundant elements. To enhance the value of dimensionless thermoelectric figure of merit ZT of cubic SrSi2, partial substitution of Sr atoms with Ba atoms was examined. Cubic Ba-substituted SrSi2, Sr1-xBaxSi2 (x = 0.00, 0.09, and 0.19), was synthesized by spark plasma sintering at 250 MPa and 1023 K, and its thermoelectric properties, such as electrical resistivity ρ, Seebeck coefficient S, and thermal conductivity κ, were measured at temperatures ranging from 10 to 380 K. The sample with Ba content x above the Ba solid solubility limit in cubic SrSi2 (0.13) was successfully synthesized. With increasing x, ρ, and S increase while κ decreases, leading to an increase of ZT with x. ZT exhibits a maximum at a temperature Tmax, which shifts from 313 to 357 K when x increases from 0 to 0.19. The maximum ZT value for cubic Sr0.81Ba0.19Si2 in the present study was calculated to be 0.21 at 357 K. The ZT value obtained is higher than previously reported values for cubic Sr1-xBaxSi2 and cubic Sr1-xCaxSi2. These results demonstrate that cubic SrSi2 has properties suitable for low temperature applications.

Three independent components of critical current density, one for the $H//c$ axis and the other two for the $H//ab$ plane, have been studied in ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$ single crystals. When the magnetic field is applied along the $c$ axis, we observed fish-tail-like peaks in the $M\ensuremath{-}H$ hysteresis loop, and the magnetization at higher temperatures exceeds that at lower temperatures at high fields. When the field is applied parallel to the $ab$ plane, a dip structure is observed in the $M\ensuremath{-}H$ hysteresis loop near the self-field. In addition, for the $H//ab$ plane, we succeeded in separately evaluating the large and significantly anisotropic in-plane and out-of-plane ${J}_{\mathrm{c}}$. Transmission electron microscopy revealed the presence of planar defects parallel to the $ab$ plane in ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, which have not been observed in any other iron-based superconductors. We discuss the possible relationship between the anomalous ${J}_{\mathrm{c}}$ behavior and the planar defects.

The lossless current-carrying capacity of a superconductor is limited by its critical current density (Jc). A key to enhance Jc towards real-life applications is engineering defect structures to optimize the pinning landscape. For iron-based superconductors (IBSs) considered as candidate materials for high-field applications, high Jc values have been achieved by various techniques to introduce artificial pinning centres. Here we report extraordinary vortex pinning properties in CaKFe4As4 (CaK1144) arising from the inherent defect structure. Scanning transmission electron microscopy revealed the existence of nanoscale intergrowths of the CaFe2As2 phase, which is unique to CaK1144 formed as a line compound. The Jc properties in CaK1144 are found to be distinct from other IBSs characterized by a significant anisotropy with respect to the magnetic field orientation as well as a remarkable pinning mechanism significantly enhanced with increasing temperature. We propose a comprehensive explanation of the Jc properties based on the unique intergrowths acting as pinning centres., Comment: 15 pages, 5 figures, and Supplementary Information. One literature on the calculation of anisotropic Jc [S. Pyon, et al. Phys. Rev. B 99, 104506 (2019)] was added to the reference list

Sc2Ru3Si4, monoclinic, C2/c (no. 15), a = 19.0663(5) Å, b = 5.27810(10) Å, c = 13.3458(4) Å, β = 127.7710(10)°, V = 1061.62(5) Å3, Z = 8, R gt(F) = 0.0209, wR ref(F 2) = 0.0530, T = 293(2) K.

The thermal expansion of β-FeSi2 and Mg2Si was investigated at high temperatures (ranging from 300 to 1173 K for β-FeSi2 and from 293 to 873 K for Mg2Si) using powder X-ray diffraction. The linear thermal expansion coefficients αL for the three lattice parameters of β-FeSi2 range from 10.6(2) to 11.8(4) × 10−6 K−1, which indicates small anisotropy, which is in contrast to the large anisotropy reported previously. The volumetric thermal expansion coefficient αV for β-FeSi2 is relatively large among the transition-metal disilicides. αL for Mg2Si can be expressed by the linear expression of T: αL = 11(1) × 10−6 + 6.9(2) × 10−9T K−1. αV for Mg2Si is larger than that of the transition-metal disilicides, including β-FeSi2. Based on a comparison of αL among Mg2Si, several metals and silicides, the candidates for electrode materials are discussed. In particular, temperature dependence and value of αL for Ni is close to those for Mg2Si, which suggests that Ni is a good candidate electrode material with respect to thermal expansion.

SrGe 2 and BaGe 2 were characterized for structural, electronic and optical properties by means of diffuse reflectance and first-principles density functional theory. These two germanides crystallize in the BaSi 2 -type structure, in which Ge atoms are arranged in tetrahedral configuration. The calculation indicates a charge transfer from Sr (or Ba) atoms to Ge atoms along with the formation of covalent bonds among Ge atoms in Ge tetrahedral. The computational results confirm that these two germanies are Zintl phase described as Sr 2 Ge 4 (or Ba 2 Ge 4 ), which are characterized by positively charged [Sr 2 (or Ba 2 )] 2.59+ and negatively charged [Ge 4 ] 2.59− units acting as cation and anion, respectively. These compounds are indirect gap semiconductors with band gap estimated to be E g = 1.02 eV for BaGe 2 and E g = 0.89 eV for SrGe 2 which are in good agreement with our experimental measured values ( E g = 0.97 eV for BaGe 2 and E g = 0.82 eV for SrGe 2 ). Our calculations demonstrate that the band gaps are narrowed by application of hydrostatic pressure; the pressure coefficients are estimated to be −10.54 for SrGe 2 and −10.06 meV/GPa for BaGe 2 . Optical properties reveal that these compounds have large absorption coefficient (∼7.5 × 10 4 cm −1 at 1.5 eV) and the estimated high frequency (static) dielectric constant are, e ∞ ( e 0 ) ≈ 12.8(20.97) for BaGe 2 and e ∞ ( e 0 ) ≈ 14.27(22.87) for SrGe 2 .

SrGe2 and BaGe2 were synthesized by Ar arc-melting, and their energy gap Eg was evaluated using diffuse reflectance measurements. SrGe2 and BaGe2 were revealed to be semiconductors with an Eg of 0.82 and 0.97 eV, respectively. Since SrGe2 and BaGe2 are isostructural with BaSi2, the formation of a Ba1-xSrx Si2-yGey solid solution is expected. This result of Eg evaluation suggests that the formation of a Ba1-xSrx Si2-yGey solid solution makes it possible to tune Eg from 0.82 to 1.20 eV because Ba0.59Sr0.41Si2 has been previously reported to have an Eg of 1.20 eV. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Two kinds of magnesium-based compounds Mg9Si5 and Mg4Si3Al have been prepared under high pressure and high temperature (HPHT) conditions of 5 GPa at 900-1100 °C. Single crystal study revealed that Mg9Si5 crystallizes in space group P6(3) (No. 173) with the lattice parameters a = 12.411(1) Å, c = 12.345(1) Å, and Z = 6. The structure can be derived from the high pressure form Mg2Si with the anticotunnite structure; excess Si atoms of Mg9Si5 form Si-Si pairs in the prismatic cotunnite columns running along the c axis. Mg4Si3Al is obtained by a rapid cooling of a ternary mixture Mg:Al:Si = 1:1:1 from ~800 °C to room temperature under a pressure of 5 GPa. The compound crystallizes in space group P4/ncc (No. 130) with the lattice parameters a = 6.7225(5) Å, c = 13.5150(9) Å, and Z = 4. The structure consists of an alternate stacking of [AlSi2] layers having a Cairo pattern and [Mg4Si] antitetragonal prismatic layers. It can be viewed as composed of hexa-Si-capped tetragonal prismatic cages Mg8Si6 with an Al atom at the center of each cage, Al@Mg8Si6. The compound shows superconductivity with a transition temperature Tc = 5.2 K. The formation regions of the two kinds of new magnesium-based compounds have been proposed.

Basic properties, such as the phase relationship, crystal structure, and energy gap Eg, have been investigated in Sr-rich Sr1 − xBaxSi2. Sr1 − xBaxSi2 (0 ≤ x ≤ 1.0) has two phases: one with the SrSi2-type structure and another with the BaSi2-type structure. The SrSi2 phase exists at x ranging from 0 to 0.13, and the BaSi2 phase exists at x ranging from 0.24 to 1.0. The volume increases with x in both the SrSi2 and BaSi2 phases. A volume jump of 13.7% appears at the structural phase transition from the SrSi2 phase to the BaSi2 phase. Eg increases with x in SrSi2-phase Sr1 − xBaxSi2 but Eg decreases with x in the BaSi2-phase Sr1 − xBaxSi2. In Sr-rich BaSi2-phase Sr1 − xBaxSi2, Ba atoms at a specific crystallographic site, the A1 site, are preferentially substituted by Sr atoms, as well as in Ba-rich BaSi2-phase Sr1 − xBaxSi2.

We have calculated the band structures of Si clathrate, M8Si38Ga8 (M = Na, K, Rb, and Cs), using the density-functional theory under the generalized gradient corrected local density approximation, where M is the encapsulated guest alkali atom. They are found to be indirect semiconductors with the calculated gaps (Eg) from 0.45 to 0.89 eV, which should be compared to the calculated gap of 0.65 eV of crystalline Si with the diamond structure. The gaps become wider with the promotion to the heavier guest alkali atoms and the reasons of gap widening are discussed using the calculated dependence of Eg on the cell-volume of guest-free silicon clathrate (Si46). Effect of the substitutional elements in the clathrate framework (Al and In in place of Ga) was also discussed.

We investigated the phase stability and superconducting properties of YbGaxSi2−x. Polycrystalline samples were synthesized by argon arc melting and subsequent annealing. The composition range of the phase with the AlB2-type structure was determined to be 1.12(1) ≤ x ≤ 1.49(3) by powder X-ray diffraction and electron probe microanalysis. The lattice constants, both a and c, increase linearly with x throughout the single-phased region. Electrical resistivity showed metallic behavior for all samples, and the superconducting transition was observed to occur at critical temperatures ranging from TC = 2.4 K for x = 1.15 to less than 1.8 K for x = 1.41. The extent of the decrease in TC with x is comparable to that in MGaxSi2−x (M = Ca, Sr, Ba) for x > 1. The negative sign of the Seebeck coefficient measured for x = 1.20 indicates that the dominant carriers are electrons. The temperature dependence of the magnetic susceptibility below room temperature showed almost nonmagnetic behavior suggesting the nearly dival...

The crystal structure and energy gap of Ba1−xSrxSi2 (x = 0.20 and 0.41), a promising material for solar cells, have been investigated. Ba1−xSrxSi2 has the BaSi2-type structure (orthorhombic, Pnma, Z = 8, a = 8.8258(7), b = 6.6736(4), c = 11.4364(8) A for x = 0.20, a = 8.7466(4), b = 6.6278(3), c = 11.3553(5) A for x = 0.41). The unit cell volume decreases with respect to the Sr content x. Ba atoms at a specific crystallographic site, A1 site, are substituted by Sr atoms preferentially. As a result, The Sr substitution deforms BaSi2 inhomogeneously; the Sr substitution of 41% reduces the volume of coordination polyhedra of A1 and A2 atoms by 5.9 and 4.4%, respectively, while it reduces the volume of Si tetrahedron by a small amount, less than 1%. Diffuse reflectance spectroscopy has demonstrated that the energy gap increases with Sr content x, which is qualitatively consistent with the previous results obtained using Ba1−xSrxSi2 epitaxal thin films.

The nitridation process of Eu-doped AEAlSi (AE=Ca and/or Sr) was investigated by thermogravimetry–differential thermal analysis to improve the method for synthesis of AEAlSiN3:Eu2+ nitride phosphors. The nitridation reactivity was dependent on alkaline earth elements. For SrxEuyCa1−x−yAlSi with a high Sr content, nitridation proceeded efficiently at 1100°–1150°C, close to the melting point of the intermetallic compounds. As nitridation of Si or Al intermetallics usually proceeds via the diffusion-controlled surface reaction, sudden rupture of the diffusion barrier, the surface nitride layer, at the melting point could cause a marked change in the reaction rate and dependence on nitrogen partial pressure. The order of reactivity at temperatures close to the melting point agreed with the order of vapor pressure of alkaline earth elements at the melting point. A highly efficient process for large-scale production of SrxCa1−xAlSiN3:Eu2+ phosphor was developed taking advantage of the characteristic nitridation reaction at the melting point.

The ternary silicides LaAl2−xSix with x ranging from 0 to 1.03 were synthesized by Ar-arc melting. The crystal structure of LaAl2−xSix depends on the Si content x: the Cu2Mg-type structure for 0 ≤ x ≤ 0.005, the AlB2-type for 0.14 ≤ x ≤ 0.62, and the α-ThSi2-type for 0.72 ≤ x ≤ 1.03. The range of x at which the AlB2 phase appears was wider than that reported previously. In the AlB2 phase, the lattice constants a and c change anisotropically with x: a decreases with x, while c increases with x. On the other hand, in the α-ThSi2 phase, both a and c decrease with x. The electrical resistivity measurements at temperatures ranging from 2 to 300 K revealed that the AlB2 phase and the α-ThSi2 phase LaAl2−xSix are metals that show no superconductivity down to 2 K.

A magnetization study on the superconducting filled skutterudite La0.8Rh4P12 has revealed the lower critical field HC1(0) of 71(2) Oe and the upper critical field HC2(0) of 126(7) kOe. Using these values, the coherent length ξ(0), penetration depth λ(0) and Ginzburg–Landau parameter κ(0) were determined to be 5.1(1) nm, 3.1(2) × 102 nm and 60(3), respectively. The estimated critical current was 18.4 kA cm−2 at 4.2 K and 0 kOe using the Bean model.

Electrical resistance measurements at temperatures ranging from 4.2 to 300 K and pressures ranging from 0 to 3.6 GPa indicate that pressurization reduces the energy gap E g with a pressure coefficient, ⅆ E g /ⅆ P , of −8.8(4) meV/GPa. The deformation potential of E g is estimated to be 0.50(2) eV, which is smaller than that of tetrahedrally bonded semiconductors, such as Si (1.46 eV). The reduction of E g by pressurization is qualitatively consistent with the results of a previously reported calculation [Imai Y, Watanabe A. Intermetallics 2006;14:666].

The development of a disposal technique for the radiotoxic {sup 137}Cs in nuclear wastes is one of the most urgent issues in nuclear fuel technology. An effective disposal method of {sup 137}Cs is to immobilize it in a synthetic rock (SYNROC) material: cesium titanate hollandite, {sup 137}Cs{sub x}Ti{sub 8}O{sub 16} (I4/m, a=10.2866(3)A, c=2.9669(1)A). Practical applications of {sup 137}Cs{sub x}Ti{sub 8}O{sub 16} have been restricted so far because the conventional synthetic method requires strong chemical reducers and reaction temperatures higher than 1250 deg. C. In this report, we present a milder preparation method of Cs{sub x}Ti{sub 8}O{sub 16} by electrolysis of a mixture of Cs{sub 2}MoO{sub 4} and TiO{sub 2} in ambient atmosphere at 900 deg. C. The Cs content in the resultant single-crystalline Cs{sub 1.35}Ti{sub 8}O{sub 16} is competitive with the highest value in polycrystalline Cs{sub 1.36+}/-{sub 0.03}Ti{sub 8}O{sub 16} prepared by the conventional synthetic method. The electrochemical preparation of Cs{sub 1.35}Ti{sub 8}O{sub 16} is a promising way to immobilize a high quantity of {sup 137}Cs ions in a stable form of single-crystalline SYNROC.

An electroplating technique of the superconductive boride MgB 2 onto graphite substrates is reported. Films of MgB 2 with a thickness of tens micrometer were fabricated on the planar and curved surfaces of graphite substrates by means of electrolysis on a mixture of magnesium chloride, potassium chloride, sodium chloride, and magnesium borate fused at 600 °C under an Ar atmosphere. The electrical resistivity and magnetization measurements revealed that the electroplated MgB 2 films undergo a superconducting transition with the critical temperature ( T c ) of 36 K.

Single crystals of Cr2O3 have been grown by means of electrolysis on a 1:100 stoichiometric mixture of CrO3 and cesium molybdate, Cs2MoO4, fused at 1000°C in an ambient atmosphere. Potentiometric measurements on the molten salts have shown the existence of a critical voltage of −320 mV below which hexagonal platelets-shaped single-crystalline Cr2O3 is grown on the surface of the working electrode. Coulometry measurements have revealed that the Cr ions are at their highest oxidation state of Cr+6 in the molten electrolyte, which suggests that the electric reduction of Cr+6 to Cr+3 drives the single-crystal growth of Cr2O3.

The structural phase transitions of alkaline-earth-metal disilicides MAESi2 (MAE = Ca, Sr, and Ba) at high pressures and high temperatures were investigated by the in situ X-ray diffraction technique. At pressures ranging from 0 to 15.5 GPa and temperatures ranging from 300 to 1300 K, CaSi2 has three high-pressure phases: EuGe2 phase, α-ThSi2 phase, and AlB2-like phase. At pressures ranging from 0 to 7.8 GPa and temperatures ranging from 300 to 1300 K, SrSi2 has a high-pressure phase, the α-ThSi2 one. BaSi2 was confirmed to have three high-pressure phases, the SrSi2, the EuGe2, and BaSi2-IV, in the pressure−temperature region ranging from 0 to 9.5 GPa and from 300 to 1300 K. In MAESi2, the structures that appear at high pressures are the same as those of alkaline-earth disilicides or rare-earth disilicides with a smaller volume per chemical formula unit under ambient conditions. The observed structural sequence is different from that already known in other AX2-type compounds. This is due to the fact that ...

We have investigated the band structure of K8Ga8Si38 clathrates by using optical reflectance measurements and first-principle calculations based on the density functional theory. The imaginary part of the dielectric function e2 was calculated from the normal reflectance spectrum via the Kramers-Kronig analysis. The experimental e2 values showed a fundamental absorption edge near 1 eV. From the analysis of the absorption spectrum, we found that the value of the absorption edge energy is approximately 1.2 eV for a K8Ga8Si38 clathrate crystal.

A filled skutterudite, La$_{0.5}$Rh$_4$Sb$_{12}$, with a lattice constant of 9.284(2) {\AA} was synthesized using a high-pressure technique. The electrical resistivity showed semiconducting behavior and the energy gap was estimated to be more than 0.08 eV. Magnetic susceptibility measurements indicated temperature-independent diamagnetism, which originates from Larmor diamagnetism. The electrical properties of this compound are more similar to those of the La$_{0.5}$Rh$_4$As$_{12}$ semiconductor with an energy gap of 0.03 eV than to those of the La$_{0.6}$Rh$_4$P$_{12}$ superconductor., Comment: 12 pages, 3 figures

A polycrystalline sample of PrInNi 4 with the cubic MgSnCu 4 -type structure has been prepared. Magnetization M and electrical resistivity ρ have been investigated as functions of temperature T and magnetic field H . M and ρ vs. T for H 0.65 T, M and ρ vs. T indicate the evolution of a ferromagnetic ordered state below about 3 K. At low temperature, M vs. H demonstrates a sharp increase around H =0.65 T. These phenomena are discussed in terms of a ferromagnetic transition accompanied by an abrupt mixing of crystal-field levels.

Ternary silicides A(Ga x ,Si 1− x ) 2 (A=Ca, Sr, and Ba) were prepared by Ar arc melting. Powder X-ray diffraction indicates that they have the AlB 2 -type structure in which Si and Ga atoms are arranged in chemically disordered honeycomb layers and atoms A are intercalated between them. Resistivity and DC magnetization measurements revealed that they are superconductors with a critical temperature for superconductivity ranging from 3.3 to 3.9 K.

Single crystals of silver-lead oxide Ag 5 Pb 2 O 6 have been grown from the fusion of a 5:2 stoichiometric mixture of silver nitrate Ag(NO 3 ) and lead nitrate Pb(NO 3 ) 2 at an ambient pressure. The high oxidation ability of nitrates has enabled the formation of Ag 5 Pb 2 O 6 at an ambient pressure, although Ag 5 Pb 2 O 6 has been conventionally prepared only by means of high-pressure synthesis methods.