Dielectric nonlinearity and spontaneous polarization of KTa sub 1 minus x Nb sub x O sub 3 in the diffuse transition range

KTa{sub 1{minus}{ital x}}Nb{sub {ital x}}O{sub 3} (KTN) in an intermediate-concentration range ({ital x}=15.7%) has been studied using dielectric-constant and spontaneous-polarization measurements. A large peak in the dielectric constant ({epsilon}{sub max}{congruent}70 000) is observed at the tempe...

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Bibliographic Details
Published in:Physical review. B, Condensed matter Condensed matter, 1991-04, Vol.43:10
Main Authors: Toulouse, J., Wang, X.M., Knauss, L.A., Boatner, L.A.
Format: Article
Language:English
Subjects:
360603 - Materials- Properties
ALKALI METAL COMPOUNDS
AMINES
AMMONIUM COMPOUNDS
DIELECTRIC PROPERTIES
ELECTRICAL PROPERTIES
FERROELECTRIC MATERIALS
MATERIALS SCIENCE
NIOBATES
NIOBIUM COMPOUNDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PERMITTIVITY
PHASE STUDIES
PHYSICAL PROPERTIES
POLARIZATION
POTASSIUM COMPOUNDS
QUATERNARY COMPOUNDS
REFRACTORY METAL COMPOUNDS
TANTALUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
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Summary:KTa{sub 1{minus}{ital x}}Nb{sub {ital x}}O{sub 3} (KTN) in an intermediate-concentration range ({ital x}=15.7%) has been studied using dielectric-constant and spontaneous-polarization measurements. A large peak in the dielectric constant ({epsilon}{sub max}{congruent}70 000) is observed at the temperature {ital T}{sub {ital c}}{sup *}. From room temperature down to {ital T}{sub {ital c}}{sup *}+20 K, {epsilon} obeys a Curie-Weiss law with {ital T}{sub 0}{similar to}142.3 K. Below, {epsilon} deviates from this law and {ital P}-{ital E} hysteresis loops are observed. These results indicate that the phase transition exhibits a diffuse character which is related to the appearance of microscopic polarized regions or cells. The {epsilon} peak at {ital T}{sub {ital c}}{sup *} exhibits a cusp shape and becomes flattened upon application of low dc-bias fields. A corresponding dielectric loss peak is also observed, the position of which reveals the relaxational character of the transition. Through measurements of {epsilon}({ital E},{ital T}) for different dc-bias fields, we have characterized the dielectric nonlinearities in the transition range; the first nonlinear coefficient, {epsilon}{sup (2)}, diverges in two distinct ranges, as ({ital T}{minus}{ital T}{sub {ital c}}{sup *}){sup {minus}{ital n}}, with {ital n}{similar to}9 initially and with {ital n}{congruent}2 closer to {ital T}{sub {ital c}}{sup *}. These results suggest that diffuse phase transitions in mixed ferroelectrics are due to the ordering of polar cells modified by mutual strain interactions.
ISSN:0163-1829
1095-3795
DOI:10.1103/PhysRevB.43.8297