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Title: Pressure-induced phase transitions in acentric BaHf(BO{sub 3}){sub 2}

High-pressure Raman scattering studies revealed that BaHf(BO{sub 3}){sub 2} is more compressible than calcite-type orthoborates and calcite, aragonite or dolomite carbonates. It undergoes a first-order reversible pressure-induced phase transition in the 3.9–4.4 GPa pressure range. Second structural change is observed at 9.2 GPa. The intermediate phase is most likely trigonal. However, Raman results suggest increase in the number of distinct BO{sub 3} groups from two in the ambient pressure phase to at least three in the intermediate phase. This intermediate phase is also strongly compressible and strong pressure dependence of the lattice modes proves that the main changes under pressure occur within the layers built from BaO{sub 6} and HfO{sub 6} octahedra. The second phase transition leads most likely to lowering of the trigonal symmetry, as evidenced by significant increase of the number of observed bands. The pressure coefficients of the Raman bands of the high-pressure phase are relatively small, suggesting more dense arrangement of the metal–oxygen polyhedra and BO{sub 3} groups in this phase. It is worth noting that the high-pressure phase was not reached in the second compression experiment up to 10 GPa. This behavior can be most likely attributed to worse hydrostatic conditions of the first experiment.more » - Graphical abstract: Raman spectra of BaHf(BO{sub 3}){sub 2} recorded at different pressures during compression showing onset of pressure-induced phase transitions. - Highlights: • High-pressure Raman spectra were measured for BaHf(BO{sub 3}){sub 2.} • BaHf(BO{sub 3}){sub 2} undergoes a reversible first-order phase transition at 3.9–4.4 GPa into a trigonal phase. • The intermediate trigonal phase is strongly compressible second structural transformation is observed at 9.2 GPa under non-perfect hydrostatic conditions.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [4]
  1. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland)
  2. Departamento de Física, Universidade Federal do Piauí, Teresina, PI 64049-550 (Brazil)
  3. Departamento de Fisica, Universidade Federal do Ceara, Fortaleza CE-60455-970 (Brazil)
  4. Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Street, 00-908 Warszawa (Poland)
Publication Date:
OSTI Identifier:
22486743
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 228; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ARAGONITE; BARIUM OXIDES; BORATES; CALCITE; CARBONATES; COMPRESSION; DOLOMITE; HAFNIUM COMPOUNDS; PHASE TRANSFORMATIONS; PRESSURE COEFFICIENT; PRESSURE DEPENDENCE; RAMAN EFFECT; RAMAN SPECTRA; RAMAN SPECTROSCOPY