High-pressure polymorphs of TbVO4: A Raman and ab initio study

Raman measurements on TbVO4 show the occurrence of three pressure-induced phase transitions. The first one, an irreversible transition from the zircon to the scheelite structure, occurs beyond 6.7 GPa. In addition, two reversible transformations take place at 26.7 and 34.4 GPa. The last transition was never reported before. The experimental findings are supported by structural and lattice-dynamics calculations that helped us to identify the post-scheelite phase as a monoclinic fergusonite structure. According to the calculations, the third transition involves a symmetry increase. An orthorhombic structure is proposed for the phase found above 34.4 GPa. The results have been compared with previous studies in TbVO4 and discussed in comparison with related compounds. The calculated equations of state are reported for the different polymorphs of TbVO4. A compressibility increase is caused by the third transition. It is associated to a bond-strength decrease, which is related to a coordination increase and a delocalization of Tb f-electrons. (C) 2013 Elsevier B.V. All rights reserved.Research supported by the Spanish MINECO (Grants No.: MAT2010-21270-C04-01/03/04), MALTA Consolider (CSD2007-00045), and Vicerrectorado de Investigacion y Desarrollo of UPV (UPV2011-0966/0914). The authors also acknowledge the computing time provided by Red Espanola de Supercomputacion and MALTA-Cluster.Errandonea, D.; Manjón Herrera, FJ.; Muñoz, A.; Rodríguez-Hernández, P.; Panchal, V.; Achary, SN.; Tyagi, AK. (2013). High-pressure polymorphs of TbVO4: A Raman and ab initio study. Journal of Alloys and Compounds. 577:327-335. https://doi.org/10.1016/j.jallcom.2013.06.008S32733557

High-pressure study of ScVO4 by Raman scattering and ab initio calculations

We report results of experimental and theoretical lattice-dynamics studies on scandium orthovanadate up to 35 GPa. Raman-active modes of the low-pressure zircon phase are measured up to 8.2 GPa, where the onset of an irreversible zircon-to-scheelite phase transition is detected. Raman-active modes in the scheelite structure are observed up to 16.5 GPa. Beyond 18.2 GPa we detected a gradual splitting of the Eg modes of the scheelite phase, indicating the onset of a second phase transition. Raman symmetries, frequencies, and pressure coefficients in the three phases of ScVO4 are discussed in the light of ab initio lattice-dynamics calculations that support the experimental results. The results on all the three phases of ScVO4 are compared with those previously reported for related orthovanadates.We acknowledge the financial support of the Spanish MCYT under Grants No. MAT2007-65990-C03-01/03, No. MAT2010-21270-C04-01/03/04, and No. CSD2007-00045, and the computation time provided by the Red Espanola de Supercomputacion and the supercomputer Atlante. F.J.M. acknowledges also financial support from "Vicerrectorado de Innovacion y Desarrollo de la UPV" (No. PAID-05-2009 through Project No. UPV2010-0096). Some of the authors are members of the MALTA Consolider Team.Panchal, V.; Manjón Herrera, FJ.; Errandonea, D.; Rodriguez-Hernandez, P.; López-Solano, J.; Muñoz, A.; Achary, S.... (2011). High-pressure study of ScVO4 by Raman scattering and ab initio calculations. Physical Review B. 83(6):641111-1-64111-10. https://doi.org/10.1103/PhysRevB.83.064111S641111-164111-10836Shafi, S. P., Kotyk, M. W., Cranswick, L. M. D., Michaelis, V. K., Kroeker, S., & Bieringer, M. (2009). In Situ Powder X-ray Diffraction, Synthesis, and Magnetic Properties of the Defect Zircon Structure ScVO4−x. Inorganic Chemistry, 48(22), 10553-10559. doi:10.1021/ic900927jMullica, D. F., Sappenfield, E. L., Abraham, M. M., Chakoumakos, B. C., & Boatner, L. A. (1996). Structural investigations of several LnVO4 compounds. Inorganica Chimica Acta, 248(1), 85-88. doi:10.1016/0020-1693(95)04971-1Errandonea, D., & Manjón, F. J. (2008). Pressure effects on the structural and electronic properties of ABX4 scintillating crystals. Progress in Materials Science, 53(4), 711-773. doi:10.1016/j.pmatsci.2008.02.001Aldred, A. T. (1984). Cell volumes of APO4, AVO4, and ANbO4 compounds, where A = Sc, Y, La–Lu. Acta Crystallographica Section B Structural Science, 40(6), 569-574. doi:10.1107/s0108768184002718Errandonea, D., Lacomba-Perales, R., Ruiz-Fuertes, J., Segura, A., Achary, S. N., & Tyagi, A. K. (2009). High-pressure structural investigation of several zircon-type orthovanadates. 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Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 32(7), 1957-1959. doi:10.1107/s0567740876006869Lacomba-Perales, R., Martinez-García, D., Errandonea, D., Le Godec, Y., Philippe, J., Le Marchand, G., … López-Solano, J. (2010). Experimental and theoretical investigation of the stability of the monoclinicBaWO4-II phase at high pressure and high temperature. Physical Review B, 81(14). doi:10.1103/physrevb.81.144117Tschauner, O., Errandonea, D., & Serghiou, G. (2006). Possible superlattice formation in high-temperature treated carbonaceous MgB2 at elevated pressure. Physica B: Condensed Matter, 371(1), 88-94. doi:10.1016/j.physb.2005.09.042Errandonea, D., Kumar, R. S., Ma, X., & Tu, C. (2008). High-pressure X-ray diffraction study of SrMoO4 and pressure-induced structural changes. Journal of Solid State Chemistry, 181(2), 355-364. doi:10.1016/j.jssc.2007.12.010Errandonea, D., Santamaria-Perez, D., Grover, V., Achary, S. N., & Tyagi, A. K. (2010). High-pressure x-ray diffraction study of bulk and nanocrystalline PbMoO4. Journal of Applied Physics, 108(7), 073518. doi:10.1063/1.3493048Errandonea, D., Santamaria-Perez, D., Bondarenko, T., & Khyzhun, O. (2010). New high-pressure phase of HfTiO4 and ZrTiO4 ceramics. Materials Research Bulletin, 45(11), 1732-1735. doi:10.1016/j.materresbull.2010.06.061Marqués, M., Flórez, M., Recio, J. M., Gerward, L., & Olsen, J. S. (2006). Structure and stability ofZrSiO4under hydrostatic pressure. Physical Review B, 74(1). doi:10.1103/physrevb.74.014104Lacomba-Perales, R., Errandonea, D., Meng, Y., & Bettinelli, M. (2010). High-pressure stability and compressibility ofAPO4(A=La, Nd, Eu, Gd, Er, and Y) orthophosphates: An x-ray diffraction study using synchrotron radiation. Physical Review B, 81(6). doi:10.1103/physrevb.81.064113Long, Y. W., Zhang, W. W., Yang, L. X., Yu, Y., Yu, R. C., Ding, S., … Jin, C. Q. (2005). Pressure-induced structural phase transition in CaCrO4: Evidence from Raman scattering studies. Applied Physics Letters, 87(18), 181901. doi:10.1063/1.2117624Long, Y. W., Yang, L. X., Yu, Y., Li, F. Y., Yu, R. C., Ding, S., … Jin, C. Q. (2006). High-pressure Raman scattering and structural phase transition inYCrO4. Physical Review B, 74(5). doi:10.1103/physrevb.74.054110Errandonea, D., Kumar, R. S., Gracia, L., Beltrán, A., Achary, S. N., & Tyagi, A. K. (2009). Experimental and theoretical investigation ofThGeO4at high pressure. Physical Review B, 80(9). doi:10.1103/physrevb.80.094101Gracia, L., Beltrán, A., & Errandonea, D. (2009). Characterization of theTiSiO4structure and its pressure-induced phase transformations: Density functional theory study. Physical Review B, 80(9). doi:10.1103/physrevb.80.094105Errandonea, D. (2007). Landau theory applied to phase transitions in calcium orthotungstate and isostructural compounds. 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Zircon to monazite phase transition in CeVO4

X-ray diffraction and Raman-scattering measurements on cerium vanadate have been performed up to 12 and 16 GPa, respectively. Experiments reveal that at 5.3 GPa the onset of a pressure-induced irreversible phase transition from the zircon to the monazite structure. Beyond this pressure, diffraction peaks and Raman-active modes of the monazite phase are measured. The zircon to monazite transition in CeVO4 is distinctive among the other rare-earth orthovanadates. We also observed softening of external translational Eg and internal B2g bending modes. We attributed it to mechanical instabilities of zircon phase against the pressure-induced distortion. We additionally report lattice-dynamical and total-energy calculations which are in agreement with the experimental results. Finally, the effect of non-hydrostatic stresses on the structural sequence is studied and the equations of state of different phases are reported.Comment: 45 pages, 8 figures, 8 table

High-pressure lattice-dynamics of NdVO4

High-pressure Raman-scattering measurements and ab initio calculations on NdVO4 have been carried out up to 30 GPa. Our combined experimental and theoretical study confirms that beyond 5.9 GPa NdVO4 undergoes an irreversible zircon to monazite transition. The coexistence of zircon and monazite phases is experimentally observed up to ~8 GPa (which agrees with the theoretical transition pressure), stabilizing the monazite phase as a single phase around 10 GPa. Calculations additionally predict the existence of a second high-pressure phase transition at 12.4 GPa. This reversible phase transition has been experimentally observed beyond 18.1 GPa and remains stable up to 30 GPa. The post-monazite phase is predicted to have a monoclinic structure isomorphic to the BaWO4-II type structure. The calculated structure for the three polymorphs of NdVO4 is reported and the pressure dependence of their Raman modes is discussed

Experimental and theoretical investigations on the polymorphism and metastability of BiPO4

In this work we report the metastability and the energetics of the phase transitions of three different polymorphs of BiPO4, namely trigonal (Phase-I, space group P3(1)21), monoclinic monazite-type (Phase-II, space group P2(1)/n) and SbPO4-type monoclinic (Phase-III, space group P2(1)/m) from ambient and non-ambient temperature powder XRD and neutron diffraction studies as well as ab initio density functional theory (DFT) calculations. The symmetry ambiguity between P2(1) and P2(1)/m of the high temperature polymorph of BiPO4 has been resolved by a neutron diffraction study. The structure and vibrational properties of these polymorphs of the three polymorphs have also been reported in detail. Total energy calculations have been used to understand the experimentally observed metastable behavior of trigonal and monazite-type BiPO4. Interestingly, all of the three phases were found to coexist after heating a single phasic trigonal BiPO4 to 773 K. The irreversible nature of these phase transitions has been explained by the concepts of the interplay of the structural distortion, molar volume and total energy.This study was supported by the Spanish government MEC under grants no: MAT2010-21270-C04-01/04, by MALTA Consolider Ingenio 2010 project (CSD2007-00045), and by the Vicerrectorado de Investigacion y Desarrollo of the Universidad Politecnica de Valencia (UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11). S. N. A. acknowledges the support provided by Universitat de Valencia during his visit to it. A. M. and P. R.-H. acknowledge the computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster.Achary, SN.; Errandonea, D.; Muñoz, A.; Rodríguez Hernández, P.; Manjón Herrera, FJ.; Krishna, PSR.; Patwe, SJ.... (2013). Experimental and theoretical investigations on the polymorphism and metastability of BiPO4. Dalton Transactions. 42:14999-15015. https://doi.org/10.1039/c3dt51823jS14999150154

New polymorph of InVO4: A high-pressure structure with six-coordinated vanadium

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Inorganic Chemestry, copyright © American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/ic402043xA new wolframite-type polymorph of InVO4 is identified under compression near 7 GPa by in situ high-pressure (HP) X-ray diffraction (XRD) and Raman spectroscopic investigations on the stable orthorhombic InVO4. The structural transition is accompanied by a large volume collapse (Delta V/V = -14%) and a drastic increase in bulk modulus (from 69 to 168 GPa). Both techniques also show the existence of a third phase coexisting with the low- and high-pressure phases in a limited pressure range close to the transition pressure. XRD studies revealed a highly anisotropic compression in orthorhombic InVO4. In addition, the compressibility becomes nonlinear in the HP polymorph. The volume collapse in the lattice is related to an increase of the polyhedral coordination around the vanadium atoms. The transformation is not fully reversible. The drastic change in the polyhedral arrangement observed at the transition is indicative of a reconstructive phase transformation. The HP phase here found is the only modification of InVO4 reported to date with 6-fold coordinated vanadium atoms. Finally, Raman frequencies and pressure coefficients in the low- and high-pressure phases of InVO4 are reported.This research supported by the Spanish government MINECO under Grant Nos. MAT2010-21270-C04-01/04 and CSD2007-00045. O.G. acknowledges support from Vicerrectorado de Investigacion y Desarrollo of UPV (Grant No. UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11). S.N.A. acknowledges support provided by Universitat de Valencia during his visit to it. B.G.-D. acknowledges the financial support from MINECO through the FPI program.Errandonea, D.; Gomis Hilario, O.; García-Domene, B.; Pellicer Porres, J.; Katari, V.; Achary, SN.; Tyagi, AK.... (2013). New polymorph of InVO4: A high-pressure structure with six-coordinated vanadium. Inorganic Chemistry. 52(21):12790-12798. https://doi.org/10.1021/ic402043xS1279012798522

High-pressure lattice dynamical study of bulk and nanocrystalline In2O3

The effect of pressure on the vibrational properties of bulk and nanocrystallinepowders of cubic bixbyite-type In2O3 has been investigated at room temperature by means of Raman spectroscopy up to 31.6 and 30¿GPa, respectively. We have been able to follow the pressure dependence of up to sixteen and seven Raman modes in bulk and nanocrystalline cubic In2O3, respectively. The experimental frequencies and pressure coefficients of the Raman-active modes of bulk cubic In2O3 at ambient pressure are in good agreement with those predicted by our theoretical ab initio calculations. Furthermore, a comparison of our experimental data with our calculations for the Raman modes in rhombohedral corundum and orthorhombic Rh2O3-II structures and with already reported Raman modes of rhombohedral corundum-type In2O3 at room pressure indicate that Raman scattering measurements provide no experimental evidence of the cubic to rhombohedral or cubic to orthorhombic phase transitions either in bulk material or in nanocrystals up to 30¿GPa. © 2012 American Institute of PhysicsResearch financed by the Spanish MEC under Grant No. MAT2010-21270-C04-01/03/04 and from Vicerrectorado de Investigacion de la Universitat Politecnica de Valencia under Projects UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11. CONACyT Mexico under the Project J-152153-F and the Marie-Curie Intra-European Fellowship have supported AHR. Supercomputer time has been provided by the Red Espanola de Supercomputacion (RES) and the MALTA cluster. B.G.-D. acknowledges J. Ruiz-Fuertes for enlightening suggestions. We also acknowledge the financial support from the MEC through the FPI program and Juan de la Cierva fellowship.Garcia Domene, B.; Ortiz, HM.; Gomis Hilario, O.; Sans, JA.; Manjón Herrera, FJ.; Muñoz, A.; Rodríguez-Hernández, P.... (2012). High-pressure lattice dynamical study of bulk and nanocrystalline In2O3. Journal of Applied Physics. 112:1235111-1235117. https://doi.org/10.1063/1.4769747S12351111235117112Granqvist, C. G. (1993). Transparent conductive electrodes for electrochromic devices: A review. Applied Physics A Solids and Surfaces, 57(1), 19-24. doi:10.1007/bf00331211Mizoguchi, H., & Woodward, P. M. (2004). Electronic Structure Studies of Main Group Oxides Possessing Edge-Sharing Octahedra:  Implications for the Design of Transparent Conducting Oxides. Chemistry of Materials, 16(25), 5233-5248. doi:10.1021/cm049249wKing, P. D. C., Veal, T. D., Fuchs, F., Wang, C. Y., Payne, D. J., Bourlange, A., … McConville, C. F. (2009). 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Overexpression of Myocilin in the Drosophila Eye Activates the Unfolded Protein Response: Implications for Glaucoma

Glaucoma is the world's second leading cause of bilateral blindness with progressive loss of vision due to retinal ganglion cell death. Myocilin has been associated with congenital glaucoma and 2-4% of primary open angle glaucoma (POAG) cases, but the pathogenic mechanisms remain largely unknown. Among several hypotheses, activation of the unfolded protein response (UPR) has emerged as a possible disease mechanism.We used a transgenic Drosophila model to analyze whole-genome transcriptional profiles in flies that express human wild-type or mutant MYOC in their eyes. The transgenic flies display ocular fluid discharge, reflecting ocular hypertension, and a progressive decline in their behavioral responses to light. Transcriptional analysis shows that genes associated with the UPR, ubiquitination, and proteolysis, as well as metabolism of reactive oxygen species and photoreceptor activity undergo altered transcriptional regulation. Following up on the results from these transcriptional analyses, we used immunoblots to demonstrate the formation of MYOC aggregates and showed that the formation of such aggregates leads to induction of the UPR, as evident from activation of the fluorescent UPR marker, xbp1-EGFP. CONCLUSIONS / SIGNIFICANCE: Our results show that aggregation of MYOC in the endoplasmic reticulum activates the UPR, an evolutionarily conserved stress pathway that culminates in apoptosis. We infer from the Drosophila model that MYOC-associated ocular hypertension in the human eye may result from aggregation of MYOC and induction of the UPR in trabecular meshwork cells. This process could occur at a late age with wild-type MYOC, but might be accelerated by MYOC mutants to account for juvenile onset glaucoma