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Ferroelectric-to-relaxor crossover and oxygen vacancy hopping in the compositionally disordered perovskites KTa{sub 1-x}Nb{sub x}O{sub 3}:Ca

Journal Article · · Physical Review. B, Condensed Matter and Materials Physics
 [1];  [2]
  1. Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States)
  2. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6056 (United States)
+ Show Author Affiliations

It is shown that lattice disorder induced by Nb and Ca substitution has a strong influence on the dielectric and relaxational properties of KTaO{sub 3}. Both substituents are believed to occupy off-center positions at the Ta site, and the difference in valence between the Ca{sup 2+} and Ta{sup 5+} ions leads to the formation of oxygen vacancies (V{sub O}). Specifically, for a KTa{sub 1-x}Nb{sub x}O{sub 3}:Ca crystal with x=0.023 and with a 0.055 at. % Ca doping, we observe (i) a ferroelectric transition at atmospheric pressure (1 bar); (ii) a large enhancement of the transition temperature by Ca doping; (iii) a pressure-induced crossover from ferroelectric-to-relaxor behavior; (iv) the impending vanishing of the relaxor phase at high pressure; (v) the reorientation of the Ca-oxygen vacancy (Ca:V{sub O}) pair defect; and (vi) the variation of the energetics and dynamics of this reorientation with pressure. Most of these effects are associated with Nb- and Ca-induced dipolar entities and appear to be general features of soft mode ferroelectrics with random-site polar nanodomains. The ferroelectric-to-relaxor crossover can be understood in terms of a large decrease with pressure in the correlation length among polar nanodomains--a unique property of soft ferroelectric mode systems. (c) 2000 The American Physical Society.

OSTI ID:
20215482
Journal Information:
Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 6 Vol. 61; ISSN 1098-0121
Country of Publication:
United States
Language:
English

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Related Subjects

36 MATERIALS SCIENCE
CALCIUM
CRYSTAL DOPING
CRYSTAL-PHASE TRANSFORMATIONS
CURIE POINT
DIELECTRIC PROPERTIES
EXPERIMENTAL DATA
FERROELECTRIC MATERIALS
NIOBIUM OXIDES
PHASE TRANSFORMATIONS
POTASSIUM OXIDES
PRESSURE DEPENDENCE
RELAXATION
TANTALATES
TANTALUM OXIDES
THEORETICAL DATA
VACANCIES
VALENCE