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Growth morphology of carbon clusters deposited on different substrates were investigated by theoretical and experimental approach. For theoretical approach, molecular dynamics was employed to evaluate an adsorptive stability of different size of carbon clusters placed on different substrates. The adsorptive stability was estimated by the difference of total energy of supercell designed as carbon cluster placed on a certain crystal plane of substrate. Among the simulations of this study, carbon cluster flatly settled down on the surface of SrTiO$$_{3}$$ 3 (001). The result was experimentally verified with layer by layer growth of graphene by pulsed laser deposition in carbon dioxide atmosphere. The absorptive stability can be useful reference for screening substrate for any target material other than graphene.

Valence stability of aliovalent ions is mostly correlated with lattice site potential in ionic crystals. Madelung electrostatic potential is obtained by adding all the lattice site potentials for all the ions present in a crystal structure. Therefore, valence stability and the stability of a crystal structure can be better understood with consideration of both the lattice site potential and Madelung electrostatic potential. This was first demonstrated more than four decades ago by one of the present authors. We revisit this situation by using re-calculated lattice site potential and Madelung electrostatic potential for perovskite structure type ABO3 compounds using a new computer program VESTA. We show that the formation of a perovskite structure type compound with the general formula ABO3 (where A and B are cations and O is an oxide ion) becomes energetically favorable when it has a higher Madelung electrostatic potential than the combined Madelung electrostatic potential of parent binary compounds AO and B2O3 or BO2. It is further shown that strong lattice site potential results in stability of high valence or high valence ions can be stabilized in a lattice site with strong lattice-site potential. It further follows that certain ions experience maximum lattice site potential at the B ion lattice site of the perovskite structure when compared to other structures such as fluorite BO2, rutile BO2 and corundum B2O3. Therefore, (i) the stability of an ion with a high (and uncommon) valence state at the B site being higher than that at the A site, (ii) occurrence of point defects at A or O sites with weak lattice site potentials, respectively and (iii) instability of perovskite A4+B2+O3, and A5+B1+O3 compounds, respectively can be rationalized by lattice site potential and Madelung electrostatic potential analysis.

Valence stability of aliovalent ions is mostly correlated with lattice site potential in ionic crystals. Madelung electrostatic potential is obtained by adding all the lattice site potentials for all the ions present in a crystal structure. Therefore, valence stability and the stability of a crystal structure can be better understood with consideration of both the lattice site potential and Madelung electrostatic potential. This was first demonstrated more than four decades ago by one of the present authors. We revisit this situation by using re-calculated lattice site potential and Madelung electrostatic potential for perovskite structure type ABO

A multifunctional tandem cell has been fashioned by (i) replacing the conventional counter electrode in a n-type titanium dioxide-based quantum dot sensitized solar cell (QDSC) with a QD-sensitized p-type nickel oxide photocathode to harness maximum power-conversion efficiency, and (ii) by coating an electrochromic molybdenum oxide overlayer at the photoanode. Light harvesting In2S3 nano-flakes were deposited onto a mesoporous NiO semiconductor scaffold. On pairing with the n-QDSC, substantial gains in the photovoltaic performance were achieved owing to greater spectral utilization across the visible region. Improvements to the photoanode architecture were developed by embedding plasmonic Au NPs in the CdS QD-sensitized TiO2 layer to augment the light absorption via plasmonic and scattering effects which translated to higher photocurrent densities. A thin film of MoO3 was applied to the photoanode, which provided an electrochromic response upon illumination, due to the concurrent insertion of an electron and a cation in the MoO3 matrix. The power conversion efficiency (PCE) achieved was 6.01% for the n-QDSC half-cell (TiO2/CdS/Au/MoO3-nS2−/Sn2−-C-fabric) and 0.047% for the p-QDSC half-cell (NiO/In2S3-nS2−/Sn2−-C-fabric). A stellar PCE value of 7.99% was attained when the two half-cells were co-assembled in a tandem device, in spite of the disparity in performance between the photoanode and photocathode. The maximum transmission modulation for the tandem device under 1 sun irradiance was 34% and the photocoloration efficiency was 16.4 cm2 min−1 W−1 at 550 nm. The results highlight the potential opportunities for combining energy conversion and light management in photovoltaics based on nanotechnology.

The pyrochlore solid solution (Na0.33Ce0.67)(2)-(Ir1-xRux)(2)O-7 (0

Crystalline CrOCl3 contains [Cl2OCr(?-Cl)2CrOCl2] molecules with two square pyramidal CrOCl4 units sharing a common edge and with the Cr–O arranged anti, a new structure type for transition metal MOX3 compounds. Crystals are monoclinic with space group P21/c, Z = 4, with a = 5.735(5), b = 13.738(7), c = 11.318(4) A, ? = 90°, ? = 98.346(6)°, ? = 90°. Its IR and UV/Vis spectra are reported and compared with those of the C3v monomer found in the gas phase. Structures are also reported for M2[CrOCl5] (M = Cs or Rb) and show a pseudo-octahedral anion. Cs2[CrOCl5] adopts a K2PtCl6-type structure with [CrOCl5]2– ions randomly orientated, but Rb2[CrOCl5] is orthorhombic with space group Pnma with a = 13.6471(7), b = 9.9175(5), and c = 6.9562(4) A. Rietveld refinement of the data on the rubidium salt gave Cr–O = 1.628(1), Cr–CltransO = 2.652(7), Cr–CltransCl = 2.239(8)–2.342(3) A. Corresponding CrV oxide bromide species do not form

Reactions of Si(NHMe)4 with ammonia are effectively catalysed by small ammonium triflate concentrations, and can be used to produce free-standing silicon imide gels. Firing at various temperatures produces amorphous or partially crystallised silicon imidonitride/nitride samples with high surface areas and low oxygen contents. The crystalline phase is entirely α-Si3N4 and structural similarities are observed between the amorphous and crystallised materials.

We present a detailed characterization of the pyrochlore Bi2Ir2O7 prepared by a one-step hydrothermal synthesis route from aqueous sodium hydroxide solution of NaBiO3·2H2O and IrCl3·5H2O in the presence of Na2O2 at 240 °C. Using 5 M NaOH solution as the reaction medium, a fine powder of polycrystalline Bi2Ir2O7 with an average crystal size of 10 nm and surface area of ∼46 m2 g–1 is produced. Structure refinement against powder neutron diffraction reveals a stoichiometric pyrochlore with no evidence for significant oxide-ion defects. X-ray absorption near-edge structure (XANES) spectra recorded at both metal LIII-edges show that, although Bi is present solely as Bi3+, there is evidence for the oxidation of iridium slightly beyond +4. This would suggest some surface oxidation of iridium, which is also shown by X-ray photoelectron spectroscopy (XPS) measurements. Magnetization data, as a function of temperature, show that the system is paramagnetic down to a temperature of 2 K, while the electrical conductiv...

The hydrothermal synthesis of four bismuth titanate materials from common bismuth and titanium precursors under hydrothermal conditions is described. Reaction of NaBiO3·2H2O and anatase TiO2 in concentrated NaOH solution at 240 °C is shown to produce perovskite and sillenite phases Na0.5Bi0.5TiO3 and Bi12TiO20, depending on the ratio of metal precursors used. When KOH solution is used and a 1:1 ratio of the same precursors, a pyrochlore Bi1.43Ti2O6(OH)0.29(H2O)0.66 is formed. The use of a mixture of HNO3 and NaOH is shown to facilitate the formation of the Aurivillius-type bismuth titanate Bi4Ti3O12. The phases have been isolated separately as phase-pure powders and profile refinement of powder X-ray diffraction data allows comparisons with comparable materials reported in the literature. Analysis of Bi LIII-edge X-ray absorption near edge structure (XANES) spectra of the materials shows the oxidation state of bismuth is +3 in all of the hydrothermally derived products.

We describe a systematic study of the hydrothermal synthesis of rare-earth orthochromites, RCrO3 (R = La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu) and YCrO3. All nine of these materials can be prepared in a single step by hydrothermal treatment of an amorphous mixed-metal hydroxide at temperatures above 300 °C upon heating around 24 h, with no post-synthesis annealing needed. The as-made materials are highly crystalline powders with submicrometer particle size. In the case of LaCrO3 the addition of solution additives to the hydrothermal synthesis allows some modification of crystallite form of the material, and in the presence of sodium dodecylsulfate nanocrystalline powders are produced. Profile refinement of powder X-ray diffraction (XRD) data show that each of the RCrO3 materials adopts an orthorhombic distorted (Pbmn) perovskite structure. Detailed, magnetization studies as a function of temperature reveal the high quality of the specimens, with low temperature antiferromagnetic behavior seen by direct current...

The hydrothermal oxidation of Ce3+ in basic aqueous solution by NaBiVO3 at 240 °C produces fine powders of cerium−bismuth oxides with crystallite sizes of less than 10 nm, as observed by transmission electron microscopy (TEM). Analysis of X-ray absorption near-edge structure at the Bi LIII and Ce LIII edges confirms the reduction of Bi5+ to Bi3+ and the oxidation of Ce3+ to Ce4+, consistent with a general chemical composition CeIV1-xBiIIIxO2-(x/2) (x ≤ 0.6) for the mixed oxides. The refined cubic lattice parameters from powder neutron diffraction indicate a fluorite-like solid solution with volume that increases with Bi content. Pair distribution functions derived from total neutron scattering yield estimated values for refined particle diameters that agree with TEM, showing a decreasing crystallite diameter with increasing bismuth content, and a full analysis reveals that despite average long-range structure being described well as a fluorite solid-solution, the local structure is distorted. Thus, the sh...

Chemical approaches have emerged as the preferred means to synthesize nanostructures of various inorganic materials due to superior control over size, shape, and surface functionality. This article provides an overview of the contributions made in the authors' laboratory toward the synthesis of nanocrystals, nanowires, nanotubes, nanowalls, and other nanostructures of several inorganic materials. Thus, thiolized monodisperse metal nanocrystals have been obtained by a ligand exchange process and the stability of their 2D assemblies studied. Nanocrystals of pure CoO and ReO3 have been synthesized, for the first time, employing a one-pot solvothermal technique. The solvothermal method has also been used to obtain organic soluble nanocrystals of semiconducting materials such as CdS, CdSe, and GaN. Inorganic nanowires and nanotubes have been prepared by several soft chemical routes, including surfactant-assisted synthesis and hydrogel templating. A simple reaction between elemental Se and Te with NaBH4 in water has been utilized to obtain nanowires of Se and Te. We also describe the nebulized spray pyrolysis (NSP) technique to synthesize carbon nanotubes and nanowires of metals and III-V nitride semiconductors with improved yields. An important new technique for preparing nanocrystalline films of materials is by the reaction of the metal precursors in the organic layer at the interface of two immiscible liquids, with appropriate reagents. Nanocrystalline films of metals, alloys, and semiconductors and ultra-thin single-crystalline films of metal chalcogenides and oxides have been obtained by this technique. Apart from these, we discuss single precursor routes to iron sulfide, GeSe2, and III-V nitride nanostructures as well as the first synthesis of GaS and GaSe nanowalls and nanotubes obtained through exfoliation by laser irradiation and thermal treatment.

Soft chemistry has emerged as an important means of generating nanocrystals, nanowires and other nanostructures of semiconducting materials. We describe the synthesis of CdS and other metal chalcogenide nanocrystals by a solvothermal route. We also describe the synthesis of nanocrystals of AlN, GaN and InN by the reaction of hexamethyldisilazane with the corresponding metal chloride or metal cupferronate under solvothermal conditions. Nanowires of Se and Te have been obtained by a self-seeding solution-based method. A single source precursor based on urea complexes of metal chlorides gives rise to metal nitride nanocrystals, nanowires and nanotubes. The liquidliquid interface provides an excellent medium for preparing single-crystalline films of metal chalcogenides.

Hexagonal aluminum nitride nanocrystals have been prepared by the reaction of hexamethyldisilazane with Al cupferronate or AlCl3 under solvothermal conditions. The nanocrystals have been characterized by X-ray diffraction, transmission electron microscopy and spectroscopic methods. The nanocrystals have average diameters in the 10–20 nm range and are single-crystalline. A characteristic photoluminescence band is observed around 420 nm.

GaN nanocrystals (see Figure) of hexagonal structure and varying diameters have been prepared by the reaction of hexamethyldisilazane (HMDS) with gallium cupferron or GaCl 3 under solvothermal conditions. The nanocrystals show a size-dependent photoluminescence band in the 260-320 nm region, characteristic of quantum confinement.

We investigate the properties of GaN semiconducting nanoparticles as a potential candidate for photodetection in the solar-blind region. The photocurrent spectral response is studied spanning the range 1.6-5.5 eV. A significant fraction of the response is in the range 4-5.5 eV. The results are compared to other optical properties and the origins of the features observed in the spectra are speculated upon.

Thin films of La1−xSrxCoO3, Nd0.5Sr0.5CoO3, Gd0.5Sr0.5CoO3 and SrRuO3 have been deposited on Si(100), LaAlO3(100) and SrTiO3(100) single crystal substrates by nebulized spray pyrolysis. The films deposited on Si are generally polycrystalline, but they are highly oriented on the oxide substrates. The cobaltate films are generally not metallic, but exhibit low resistivity specially when x=0.3 and 0.5, the latter also exhibiting ferromagnetic characteristics. Films of La0.7Sr0.3CoO3 show negative magnetoresistance of 35% around 180 K. Films of SrRuO3 are metallic on Si and LaAlO3 substrates but show an insulator–metal transition on SrTiO3 around 130 K, around which temperature negative magnetoresistance is observed.

Crystalline CrOCl3 contains [Cl2OCr(?-Cl)2CrOCl2] molecules with two square pyramidal CrOCl4 units sharing a common edge and with the Cr–O arranged anti, a new structure type for transition metal MOX3 compounds. Crystals are monoclinic with space group P21/c, Z = 4, with a = 5.735(5), b = 13.738(7), c = 11.318(4) A, ? = 90°, ? = 98.346(6)°, ? = 90°. Its IR and UV/Vis spectra are reported and compared with those of the C3v monomer found in the gas phase. Structures are also reported for M2[CrOCl5] (M = Cs or Rb) and show a pseudo-octahedral anion. Cs2[CrOCl5] adopts a K2PtCl6-type structure with [CrOCl5]2– ions randomly orientated, but Rb2[CrOCl5] is orthorhombic with space group Pnma with a = 13.6471(7), b = 9.9175(5), and c = 6.9562(4) A. Rietveld refinement of the data on the rubidium salt gave Cr–O = 1.628(1), Cr–CltransO = 2.652(7), Cr–CltransCl = 2.239(8)–2.342(3) A. Corresponding CrV oxide bromide species do not form

GaMnN films with 1–3% Mn deposited on Si(100) and Al 2 O 3 (0001) substrates, by the technique of nebulized spray pyrolysis by employing acetylacetonate precursors, have been characterized by X-ray diffraction, photoluminescence spectra and other techniques. The films are ferromagnetic and show magnetic hysteresis. The ferromagnetic T C increases with the Mn content, with the 3% Mn film showing a T C of ∼250 K. Anomalous Hall effect is observed below T C where the films exhibit a small negative magnetoresistance.

A high-resolution x-ray powder diffraction study has been made of pseudo-rhombohedral and tetragonal phases in Na0.5Bi0.5TiO3 (NBT), produced via hydrothermal and conventional solidstate methods. Hydrothermal NBT exhibits significantly greater structural distortion at room\ud temperature than solid-state NBT. Peak widths and superstructure peak intensities show a phase\ud transition at 305 C, with trends suggesting that the structure tends towards cubic symmetry at this temperature. Structural refinements indicate that the transition occurs via a phase coexistence region with no clear intermediate phase. Piezoelectric data show evidence of polarisation pinning in hydrothermal NBT, interpreted as a high proportion of oxygen vacancies.

The hydrothermal synthesis of four bismuth titanate materials from NaBiO3 and TiO2 (anatase) precursors under hydrothermal conditions is described.

We report a systematic investigation of orthorhombic perovskite-type RCrO3 powder samples by Raman scattering for nine different rare earth R3+ cations (R = Y, La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu). The room-temperature Raman spectra and the associated phonon mode assignment provide reference data for structural investigation of the whole series of RCrO3 orthochromites and phonon ab-initio calculations. The assignment of the chromite spectra and comparison with Raman data on other orthorhombic perovskites allows correlating the phonon modes with the structural distortions in the RCrO3 series. In particular, two Ag modes are identified as octahedra rotation soft modes, as their positions scale linearly with the octahedra tilt angle of the CrO6 octahedra.

The lanthanoid chromites LnCrO3 (Ln: Y, La, Pr, Sm, Gd, Dy, Ho, Yb, Lu) are prepared by hydrothermal treatment (autoclave, 320—380 °C, 48 h) of an amorphous mixed-metal hydroxide precursor precipitated from aqueous KOH solutions of LnCl3 or Ln(NO3)3 and Cr(NO3)3 (70 °C, 2—3 d).

We present the results of a study of the solvothermal synthesis of mixed-metal cerium-containing oxides all prepared from CeCl3.7H2O at less than 250 ºC in single step reactions. The use of NaBiO3 in the presence of aqueous NaOH yields fluorite solid solutions Ce1-xBixO2-x/2 (x ≤ 0.6), whereas the use of either H2O2 or NaBrO3 as oxidant in the presence of TiF3 yields a Ce(IV) pyrochlore (Na0.33Ce0.67)2Ti2O7. With replacement of a fraction of the Ti reagent by Sn(IV) acetate, tin doping is possible in the pyrochlore. The materials have all been assessed for their use in catalysis by performing temperature programmed reduction (TPR) experiments under dilute hydrogen flow. The cerium-bismuth oxides show large and apparently reversible hydrogen uptake, but in situ powder X-ray diffraction shows that this is accompanied by phase separation into bismuth metal and CeO2 that occurs over 5 or more TPR cycles. In contrast, the cerium (IV) titanate pyrochlore shows reversible reduction at low temperature (150 ºC, after an activation step), which gives the material potential use as a precious metal support for catalysis: such as in the water-gas-shift reaction. Although Sn doping lowers the onset of reduction of the pyrochlore, consistent with an expanded lattice, the materials suffer from collapse to give SnO.

Multiferroic BiFeO3 ceramics have been doped with Ca and it is found that the magnetic Neel temperature (TNeel) increases as Ca concentration increases, at a rate of 0.66 K per 1% Ca (molar). The smaller ionic size of Ca compared with Bi results in a contraction of the lattice, suggesting that Ca doping can be regarded as a proxy for hydrostatic pressure, with an equivalence of 1% Ca=0.3 GPa. Combining these results, we argue that hydrostatic pressure should increase the magnetic transition temperature of BiFeO3 at a rate around [partial-derivative]TN/[partial-derivative]P~2.2 K/GPa. Our results also suggest that pressure (chemical or hydrostatic) may be used to bring the ferroelectric critical temperature Tc and the magnetic TNeel closer together, thereby enhancing magnetoelectric coupling, provided that electrical conductivity can be kept sufficiently low.

Indium nitride has attracted increasing attention in the last few years because of its properties of potential value in optoelectronic devices and other technologies.

Iridate pyrochlores of general formula M2Ir2O7have potential applications in catalysis [1]. They also often exhibit unusual magnetic and electronic properties caused by spin-orbit coupling and geometric frustration [2]. A detailed understanding of structure is necessary to enable these properties to be understood and exploited. Because of the propensity of the pyrochlore structure to accommodate structural disorder, we have chosen to utilise the technique of total scattering to examine the structure of M2Ir2O7(M = Bi, Nd). The sensitivity of our measurements to all the constituent elements is maximised by the combination of both neutron and X-ray total scattering. We find no evidence for magnetic ordering in our samples of Nd2Ir2O7, in contrast to literature reports [3]. By comparing the local structure of our samples with that of one reported to exhibit magnetic ordering, we explore the possibility of a structural origin for the differences in magnetic behaviour. We have found that synthesis method can directly influence the structure of these iridate pyrochlores. Local structural analysis provides evidences of A-site cation deficiency and partial oxidation of Ir(IV) to Ir(V) in samples produced by hydrothermal techniques. Irreversible changes to the lattice parameter upon heating these samples at 400 – 9000C further support the inference that the cation content is somewhat variable. We report the results of reverse Monte Carlo (RMC) refinements using the program RMCProfile, which is capable of simultaneously fitting to X-ray and neutron data, and therefore provides structural models of the greatest possible accuracy. We also report the results of in situ X-ray total scattering measurements which provide local-scale insight into the interesting thermal behaviour and apparent flexible cation content of these materials.

Microstructural features and oxidation states in multiferroic Lu2Fe2.1Mn0.9O7 have been investigated by neutron diffraction,transmission electron microscopy(TEM), and x-rayabsorption near edge spectroscopy. Our experimental results demonstrate the disordered distribution of Mn atoms in the FeO double (W) layers, indicating that structural modulations originate from the charge disproportionation, which is evidenced by the mixed-valence states of Fe ions.TEM measurements clearly reveal Mn doping induced chemical inhomogeneity and local distortions which are associated with the charge disproportionation in the W layers. In addition, the polarization is discussed in association with the lattice distortions and charge disproportionation.

We report the results of an exploratory synthetic study of iridium-containing materials using hydrothermal methods from simple metal salts. Three alkali-earth iridium hydroxides are isolated as phase-pure samples and their structures examined by single-crystal or powder diffraction methods: each contains Ir(IV)-centred octahedra, isolated from each other and sharing bridging hydroxides or fluoride with alkali-earth (Ca, Sr or Ba) centres. One of these hydroxides, Ca2IrF(OH)6.OH, possesses a unique open structure, consisting of a positively-charged framework that has one-dimensional channels in which infinite chains of hydrogen-bonded hydroxide anions are encapsulated. The addition of hydrogen peroxide or sodium peroxide to otherwise identical hydrothermal reactions yields dense oxide materials in which iridium is found in an oxidation state between +4 and +5: the novel oxide Na0.8Sr2.2Ir3O10.1 has a KSbO3-type structure with an iridium oxidation state of +5, while the new pyrochlore (Na0.27Ca0.59)2Ir2O6·0.66H2O contains iridium with an average oxidation state close to +4.5. Our results illustrate the utility for hydrothermal synthesis in the discovery of novel complex structures that may be inaccessible using conventional high-temperature synthesis, with control of the metal oxidation state possible with judicious choice of reagents.

A bismuth citrate precursor has been used to yield bismuth trioxide with single-crystalline one-dimensional (1D) morphologies in the temperature range of 400°-600°C. The growth process of the nanorods has been investigated using a series of experiments wherein different polymorphs of Bi 2 O 3 are developed along with the nonstoichiometric bismuth oxides. The nonstoichiometric oxides are generated in situ and facilitate the formation of metastable polymorphs and 1D nanostructures of Bi 2 O 3 .

3% and 5% Mn-doped GaN nanocrystals of different sizes, with the average diameters in the range of 4–18nm, have been prepared by two independent routes under solvothermal conditions starting with two different precursors. The reaction temperature was around 350°C in all the preparations. The nanocrystals so prepared exhibit ferromagnetism with magnetization (M) and Curie temperature (TC) values increasing with percent of Mn and particle size. The observation of ferromagnetism in Mn-doped GaN nanocrystals prepared at relatively low temperatures is of significance in understanding this potential in spintronics materials.

In an effort to find a simple and common single-source precursor route for the group 13 metal nitride semiconductor nanostructures, the complexes formed by the trichlorides of Al, Ga and In with urea have been investigated. The complexes, characterized by X-ray crystallography and other techniques, yield the nitrides on thermal decomposition. Single crystalline nanowires of AlN, GaN and InN have been deposited on Si substrates covered with Au islands by using the complexes as precursors. The urea complexes yield single crystalline nanocrystals under solvothermal conditions. The successful synthesis of the nanowires and nanocrystals of these three important nitrides by a simple single-precursor route is noteworthy and the method may indeed be useful in practice.