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Giant Volume Change and Topological Gaps in Temperature‐ and Pressure‐Induced Phase Transitions: Experimental and Computational Study of ThMo 2 O 8
Author(s) -
Xiao Bin,
Kegler Philip,
Gesing Thorsten M.,
Robben Lars,
BlancaRomero Ariadna,
Kowalski Piotr M.,
Li Yan,
Klepov Vladislav,
Bosbach Dirk,
Alekseev Evgeny V.
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201503839
Subject(s) - orthorhombic crystal system , monoclinic crystal system , crystallography , ambient pressure , polyhedron , materials science , phase transition , phase (matter) , crystal structure , topology (electrical circuits) , crystal (programming language) , tetrahedron , volume (thermodynamics) , thermodynamics , chemistry , geometry , physics , mathematics , organic chemistry , combinatorics , computer science , programming language
By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo 2 O 8 , allowing the formation of an unexpected new ThMo 2 O 8 polymorph (high‐temperature/high‐pressure (HT/HP) orthorhombic ThMo 2 O 8 ). Compared with the other three ThMo 2 O 8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP–orthorhombic ThMo 2 O 8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high‐pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo 2 O 8 phases are based on three‐dimensional (3D) frameworks constructed from corner‐sharing ThO x ( x= 6, 8, or 9) polyhedra and MoO 4 tetrahedra. The HT/HP–orthorhombic ThMo 2 O 8 , however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO 11 and MoO 4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo 2 O 8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings.