Premium
Phase Transitions in Perovskite Crystals
Author(s) -
Darlington C. N. W.
Publication year - 1976
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220760124
Subject(s) - wave vector , perovskite (structure) , condensed matter physics , phase transition , phase (matter) , condensation , phase boundary , boundary (topology) , natural bond orbital , point (geometry) , physics , chemistry , materials science , crystallography , thermodynamics , quantum mechanics , mathematical analysis , geometry , mathematics , density functional theory
Abstract Atomic displacements are analysed that occur at phase transitions in perovskites caused by the condensation of zone boundary modes. It is shown that for phases in which modes with wave vectors at the M‐point, ½ (a* + (a* + b*), and the R‐point, ½(a* + b* + c*), have condensed, static displacements associated with a normal mode with wave vector ½ + c* of the X‐point are also present. Such induced displacements are to be expected from Landau's theory of continuous phase transitions when terms that couple the parameters X , R , and M me included in the free energy expression. Such an expression is applied to (Na, K)NbO 3 , and the results derived from it are compared with the experiment.