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Title: Theory of structural phase transition in MgTi{sub 2}O{sub 4}

A theory of phase transition in MgTi{sub 2}O{sub 4} is proposed based on a study of the order-parameter symmetry, thermodynamics, and mechanisms of formation of the atomic and orbital structure of the low-symmetry MgTi{sub 2}O{sub 4} phase. The critical order parameter (which induces a phase transition) is determined. It is shown that the calculated MgTi{sub 2}O{sub 4} tetragonal structure is a result of displacements of magnesium, titanium, and oxygen atoms; ordering of oxygen atoms; and the participation of d{sub xy}, d{sub xz}, and d{sub yz} orbitals. The contribution of noncritical representations to ion displacements is proven to be insignificant. The existence of various metal clusters in the tetragonal phase has been established by calculation in correspondence with experimental data. It is shown (within the Landau theory of phase transitions) that phase states can be changed as a result of both first- and second-order phase transitions: the high-symmetry phase borders two low-symmetry phases by second-order transition lines, while the border between low-symmetry phases is a first-order transition line.
Authors:
 [1] ;  [2] ;  [1] ;  [3]
  1. South Russian State Polytechnical University (Russian Federation)
  2. Russian Academy of Sciences, South Science Centre (Russian Federation)
  3. South Federal University (Russian Federation)
Publication Date:
OSTI Identifier:
22472489
Resource Type:
Journal Article
Resource Relation:
Journal Name: Crystallography Reports; Journal Volume: 60; Journal Issue: 1; Other Information: Copyright (c) 2015 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMIC DISPLACEMENTS; ATOMS; MAGNESIUM COMPOUNDS; ORDER PARAMETERS; PHASE TRANSFORMATIONS; SOLID CLUSTERS; TETRAGONAL LATTICES; THERMODYNAMICS; TITANATES