Preparation of NZP-type Ca0.75+0.5xZr1.5Fe0.5(PO4)3-x(SiO4)x powders and ceramic, thermal expansion behavior

Ca0.75+0.5xZr1.5Fe0.5(PO4)3–x(SiO4)x (x = 0–0.5) solid solutions have been synthesized by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. As expected, the synthesized phosphatosilicates crystallize in a NaZr2(PO4)3-type structure (trigonal symmetry, sp. gr. R3c). The thermal expansion of the solid solutions has been studied by high-temperature Xray diffraction in the temperature range from 25 to 800°C. Their thermal expansion parameters have been calculated and analyzed as functions of composition. Highdensity ceramics based on the Ca0.875Zr1.5Fe0.5(PO4)2.75(SiO4)0.25 phosphatosilicate have been produced by spark plasma sintering and their structure and properties have been studied in detail.This work was supported by the Russian Science Foundation, project no. 16-13-10464: Advanced ceramic like mineral materials with improved and adjustable service characteristics: design, synthesis, study.Peer reviewe

K2Ta4O11 (“kalitantite”): a wide band gap semiconductor synthesized in molybdate flux medium

The successful application of molybdate flux for the crystal growth of complex tantalum oxide, verbi causa kalitantite, was shown at a submillimetre scale. The structure was determined via X-ray single crystal refinements (space group Rc, a = 627.32(2) pm, c = 3685.75(13) pm, V = 1256.11(7) pm3 × 10−6, Z = 6) to be an α-U3O8-type layered compound presenting the general formula Mx(Nb,Ta)3n+1O8n+3 (where n = 1 in the case of M being Na, Ca or Ag and n = 2 when M is La–Eu, Y or Bi), thus corroborating earlier studies. Experimental evaluations and complementary ab initio calculations revealed the semiconductor nature of K2Ta4O11. The former were used to explain the vibrational spectrum in the mid-infrared range of wavenumbers.SGG is grateful for financial support from ERDF and the Spanish MINECO (MAT2010-15094).Peer reviewe

Synthesis and structural relationship of complex tantalum phosphates in the flux system K₂O-P₂O₅-Ta₂O₅-MoO₃

Single crystals of K2Ta4O11 (I), K(TaO2)2PO4 (II) and K3Ta 5O11(PO4)2 (III) were synthesized by flux-aided method in the pseudo-quaternary system K2O-P 2O5-Ta2O5-MoO3. Tight interrelation of their crystal structures has been found via X-ray diffraction study. Experimental solid-state band gap measurements revealed its semiconductor nature corroborated with DFT calculations. Local structure of PO4 groups in (II) and (III) compounds was probed with 31P MAS NMR spectroscopy. © 2012 IEEE

Polyanionic identity of Ca2Zn2(V3O10)(VO4) photocatalyst manifested by X-ray powder diffraction and periodic boundary density functional theory calculations

The structure of photocatalytic and photoluminescent binary vanadate of the general formula “CaZnV2O7” has been investigated using X-ray powder diffraction. The compound is built up of isolated [V3O10], and [VO4] being this complex trivanadate–vanadate, in opposition to previous suggestions on isostructurality “CaMV2O7”, M – Mg or Co (Murashova et al., 1991, 36, 617–621). The present model has been confirmed by theoretical calculations. Thermal analysis and scanning electron microscopy have been performed, and the electronic structure analysis has been found to be in agreement with the experimental observations.Financial support from the Spanish Ministerio de Economía y Competitividad (MAT2013-40950-R), the Gobierno del Principado de Asturias (GRUPIN14-060) and the FEDER funding is acknowledged by AAB, SK and SGG. AAB and IVO acknowledge the JSPDS ICDD Grant-in-Aid program (12-02).Peer Reviewe

Development of inorganic ion exchangers for nuclear waste remediation. 1998 annual progress report

'To expand the authors efforts to provide families of inorganic ion exchangers useful on a global scale. In carrying out this objective, they will synthesize a variety of ion exchange materials, determine their structures and where necessary alter these structures to build in the desired properties. The underlying thermodynamic, kinetic and molecular basis of ion exchange behavior will be elucidated and their suitability for nuclear waste remediation will be assessed. As of September 1, 1996, they have synthesized a number of highly selective inorganic ion exchangers, determined their crystal structures and elucidated the mechanism of exchange for a number of these exchangers.

The crystal structure of visible light absorbing piezoelectric semiconductor SrNb₂V₂O₁₁ revisited: High-resolution X-ray diffraction, vibrational spectroscopy and computational study

Ferroelectric materials have a long-term track record of applications in electronics due to their spontaneous electric polarization. This property can be coupled with photoabsorption properties, resulting in a bulk photoelectric effect, the new on-the-edge domain for ferroelectric use. In this sense, considering the low bandgap of binary strontium-niobium ortho-vanadate SrNb 2 V 2 O 11 , which has recently been reported as ferroelectric, we propose here a deep experimental and computational understanding of its structural and physical properties, considered relevant for further applications. Microcrystalline SrNb 2 V 2 O 11 was prepared by a conventional solid state route, proposing a synthetic pathway deduced from thermoanalytical observations and high-temperature powder X-ray diffraction. The crystal structure (space group Cc, a = 18.15415(2) Å, b = 5.52811(6) Å, c = 9.52728(1) Å, β = 99.8033(8)°, Z = 2), successfully solved using high resolution powder X-ray diffraction, reveals the presence of distorted perovskite-like [Nb 4 V 2 O 12 ] units when preparing [Nb 2 V 2 O 11 ] sheets. By application of symmetry adapted mode analysis, the non-centrosymmetry originates from Sr atom displacements and [Nb 4 V 2 O 12 ] unit "breathing" deformations, which can be explained in terms of the group-subgroup relationship. By ground state analysis of the polytypes across possible C-centered monoclinic cells, only the present experimentally based structural model (space group Cc) can be adopted, substituting the so far reported crystallographic data. The semiconducting nature of the phase, with a direct bandgap of 2.3 eV, was determined by optical absorption measurements and confirmed computationally. By coupling Raman spectroscopy and density functional perturbation theory, the dielectric properties (ϵ riso = 55) were accurately calculated and the observed optical phonons were fully interpreted. Finally, using the Berry phase formalism, we predicted a value of spontaneous polarization of 16.6 μC cm -2 in the absence of confident existing experimental data. © The Royal Society of Chemistry

The crystal structure of visible light absorbing piezoelectric semiconductor SrNb2V2O11 revisited: high-resolution X-ray diffraction, vibrational spectroscopy and computational study

Ferroelectric materials have a long-term track record of applications in electronics due to their spontaneous electric polarization. This property can be coupled with photoabsorption properties, resulting in a bulk photoelectric effect, the new on-the-edge domain for ferroelectric use. In this sense, considering the low bandgap of binary strontium-niobium ortho-vanadate SrNb2V2O11, which has recently been reported as ferroelectric, we propose here a deep experimental and computational understanding of its structural and physical properties, considered relevant for further applications. Microcrystalline SrNb2V2O11 was prepared by a conventional solid state route, proposing a synthetic pathway deduced from thermoanalytical observations and high-temperature powder X-ray diffraction. The crystal structure (space group Cc, a = 18.15415(2) Å, b = 5.52811(6) Å, c = 9.52728(1) Å, β = 99.8033(8)°, Z = 2), successfully solved using high resolution powder X-ray diffraction, reveals the presence of distorted perovskite-like [Nb4V2O12] units when preparing [Nb2V2O11] sheets. By application of symmetry adapted mode analysis, the non-centrosymmetry originates from Sr atom displacements and [Nb4V2O12] unit “breathing” deformations, which can be explained in terms of the group–subgroup relationship. By ground state analysis of the polytypes across possible C-centered monoclinic cells, only the present experimentally based structural model (space group Cc) can be adopted, substituting the so far reported crystallographic data. The semiconducting nature of the phase, with a direct bandgap of 2.3 eV, was determined by optical absorption measurements and confirmed computationally. By coupling Raman spectroscopy and density functional perturbation theory, the dielectric properties (εriso = 55) were accurately calculated and the observed optical phonons were fully interpreted. Finally, using the Berry phase formalism, we predicted a value of spontaneous polarization of 16.6 μC cm−2 in the absence of confident existing experimental data.Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. S. K., S. G. G. and A. B. B. acknowledge the financial support from Spanish Ministerio de Economía y Competitividad (MAT2016-78155-C2-1-R). P. H. and A. A. B. are indebted to the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement no. 291803. This work is partially supported by the ICDD GiA #12-02 “Patterns of inorganic oxides and salts based on oxoanions” and Raphuel (ENE2016-79608-C2-1-R) project