ScVO4 under non-hydrostatic compression:a new metastable polymorph

Ustedes se ocupan e ver si se puede hacer de acceso público. Podria buscra el preprint al ser algo reciente.Se estudia el comportamiento bajo alta presión del vanadato de scandio, ScVO4, bajo compresión no hidrostática. El estudio se realiza mediante difracción de rayos X en polvo usando radiación sincrotrón. Se detecta una transición no reversible desde la fase zircon a la fase fergusonita alrededor de 6 GPa con una discontinuidad en el volumen de un 10%. La fase fergusonota se puede recuperar como metaestable confirmandose mediante XRD. Las simulaciones ab intio confirman los resultados experimentales. Las propiedades ópticas y la propiedades vibracionales de la fase fergusonita son discutidas. A presión ambiuente el gap de la fase zircon (fergusonita) es 2.75 eV (2.3 eV). Esto sugiere que este nuevo polimorfo metaestable del ScVO4 puede tener aplicaciones en tecnologias verdes, por ejemplo siendo usado como materal fotocatalitico para producción de hidrógeno mediante disociación de agua.The high-pressure (HP) behaviour of scandium vanadate (ScVO4) is investigated under non-hydrostatic compression. The compound is studied by means of synchrotron-based powder x-ray diffraction (XRD) and optical-absorption techniques. The occurrence of a non-reversible phase transition is detected. The transition is from the zircon structure to the fergusonitetype structure and takes place around 6 GPa with nearly 10% volume discontinuity. XRD measurements on the pressure cycled sample confirm for the first time that the fergusonitetype ScVO4 can be recovered as the metastable phase at ambient conditions. Raman spectroscopic measurements verify the metastable phase to be of a fergusonite-type phase. Theoretical calculations also corroborate the experimental findings. The fergusonite phase is found to be stiffer than the ambient-pressure zircon phase, as indicated by the observed experimental and theoretical bulk moduli. The optical properties and lattice-dynamics calculation of the fergusonite ScVO4 are discussed. At ambient pressure the band gap of the zircon (fergusonite)-type ScVO4 is 2.75 eV (2.3 eV). This fact suggests that the novel metastable polymorph of ScVO4 can have applications in green technologies; for instance, it can be used as photocatalytic material for hydrogen production by water splitting.DST, India for travel support and the Italian Government for hospitality at Elettra, Italy. This paper was partially supported by the Spanish Ministerio de Econom¿a y Competitividad (MINECO) under GrantsNo. MAT2013-46649-C04-01/03-P, MAT2016-75586-C4-1/3-P, and No.MAT2015-71070-REDC (MALTA Consolider)

Investigation on the Luminescence Properties of InMO4 (M = V5+, Nb5+, Ta5+) Crystals Doped with Tb3+ or Yb3+ Rare Earths Ions

[EN] We explore the potential of Tb- and Yb-doped InVO4, InTaO4, and InNbO4 for applications as phosphors for light-emitting sources. Doping below 0.2% barely change the crystal structure and Raman spectrum but provide optical excitation and emission properties in the visible and near-infrared (NIR) spectral regions. From optical measurements, the energy of the first/second direct band gaps was determined to be 3.7/4.1 eV in InVO4, 4.7/5.3 in InNbO4, and 5.6/6.1 eV in InTaO4. In the last two cases, these band gaps are larger than the fundamental band gap (being indirect gap materials), while for InVO4, a direct band gap semiconductor, the fundamental band gap is at 3.7 eV. As a consequence, this material shows a strong self-activated photoluminescence centered at 2.2 eV. The other two materials have a weak self-activated signal at 2.2 and 2.9 eV. We provide an explanation for the origin of these signals taking into account the analysis of the polyhedral coordination around the pentavalent cations (V, Nb, and Ta). Finally, the characteristic green (D-5(4) -> F-7(J)) and NIR (F-2(5/2) -> F-2(7/2)) emissions of Tb3+ and Yb3+ have been analyzed and explained.The authors thank the financial support from the Spanish Ministerio de Ciencia, Innovacion y Universidades, Spanish ́ Research Agency (AEI), Generalitat Valenciana, and European Fund for Regional Development (ERDF, FEDER) under grants no. MAT2016-75586-C4-1/2-P, RTI2018-101020-BI00, RED2018-102612-T (MALTA Consolier Team), and Prometeo/2018/123 (EFIMAT). P.B. acknowledges financial support from the Kempe Foundation and the Knut & Alice Wallenberg Foundation via a doctoral studentship. A.B.G. thanks the support provided by Universitat de Valencia to perform a research stay (Atraccióde Talent, VLC-CAMPUS)Botella, P.; Enrichi, F.; Vomiero, A.; Muñoz-Santiuste, JE.; Garg, AB.; Arvind, A.; Manjón, F.... (2020). Investigation on the Luminescence Properties of InMO4 (M = V5+, Nb5+, Ta5+) Crystals Doped with Tb3+ or Yb3+ Rare Earths Ions. ACS Omega. 5(5):2148-2158. https://doi.org/10.1021/acsomega.9b02862S214821585

High-Pressure Properties of Wolframite-Type ScNbO4

In this work, we used Raman spectroscopic and optical absorption measurements and first-principles calculations to unravel the properties of wolframite-type ScNbO4 at ambient pressure and under high pressure. We found that monoclinic wolframite-type ScNbO4 is less compressible than most wolframites and that under high pressure it undergoes two phase transitions at ∼5 and ∼11 GPa, respectively. The first transition induces a 9% collapse of volume and a 1.5 eV decrease of the band gap energy, changing the direct band gap to an indirect one. According to calculations, pressure induces symmetry changes (P2/c–Pnna–P2/c). The structural sequence is validated by the agreement between phonon calculations and Raman experiments and between band structure calculations and optical absorption experiments. We also obtained the pressure dependence of Raman modes and proposed a mode assignment based upon calculations. They also provided information on infrared modes and elastic constants. Finally, noncovalent and charge analyses were employed to analyze the bonding evolution of ScNbO4 under pressure. They show that the bonding nature of ScNbO4 does not change significantly under pressure. In particular, the ionicity of the wolframite phase is 61% and changes to 63.5% at the phase transition taking place at ∼5 GPa

Pressure-Driven Isostructural Phase Transition in InNbO4: In Situ Experimental and Theoretical Investigations

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/page/policy/articlesonrequest/index.html"[EN] The high-pressure behavior of technologically important visible-light photocatalytic semiconductor In.NbO4, adopting a monoclinic wolframite-type structure at ambient conditions, was investigated using synchrotron-based X-ray diffraction, Raman spectroscopic measurements, and first-principles calculations. The experimental results indicate the occurrence of a pressure-induced isostructural phase transition in the studied compound beyond 10.8 GPa. The large volume collapse associated with the phase transition and the coexistence of two phases observed over a wide range of pressure shows the nature of transition to be first-order. There is an increase in the oxygen anion coordination number around In and Nb cations from six to eight at the phase transition. The ambient-pressure phase has been recovered on pressure release. The experimental pressure volume data when fitted to a Birch-Murnaghan equation of states yields the value of ambient pressure bulk modulus as 179(2) and 231(4) GPa for the low and high-pressure phases, respectively. The pressure dependence of the Raman mode frequencies and Gruneisen parameters was determined for both phases by experimental and theoretical methods. The same information is obtained for the infrared modes from first-principles calculations. Results from theoretical calculations corroborate the experimental findings. They also provide information on the compressibility of interatomic bonds, which is correlated with the macroscopic properties of InNbO4.This research was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), the Spanish Research Agency (AEI), and the European Fund for Regional Development (FEDER) under Grant Nos. MAT2013-46649-004-01/02/03-P, MAT2016-75586-C4-1/2/3-P, and MAT2015-71070-REDC (MALTA Consolider). J.A.S. acknowledges financial support through the Ramon y Cajal Fellowship.Garg, AB.; Errandonea, D.; Popescu, C.; Martínez-García, D.; Pellicer Porres, J.; Rodríguez-Hernández, P.; Muñoz, A.... (2017). Pressure-Driven Isostructural Phase Transition in InNbO4: In Situ Experimental and Theoretical Investigations. Inorganic Chemistry. 56(9):5420-5430. https://doi.org/10.1021/acs.inorgchem.7b00437S5420543056