A new higher-order Landau–Ginzburg–Devonshire theory for KNbO3 crystal. (2nd December 2018)

• Record Type: Journal Article
• Authors: Kim, Il-Hwan; Kim, Il-Hun; Jang, Kum-Ok; Sin, Kye-Ryong; Kim, Chol-Jin
• Is Part Of: Phase transitions. Volume 91:Number 12(2018)
• Page Start: 1189
• Page End: 1205
• Publication Date: 2018-12-02
• Subjects: KNbO3 crystal -- LGD theory -- structural stability -- phase transitions -- ferroelectric properties; Phase transformations (Statistical physics) -- Periodicals; 530.47405
• DOI: 10.1080/01411594.2018.1536269
• Languages: English
• ISSNs: 0141-1594

Abstract

ABSTRACT: A Landau-Ginzburg-Devonshire(LGD) theory based on a structurally stable 8th-order potential with three varying expansion coefficients ( a 1, a 11 and a 2 ) was proposed for phenomenological description for KNbO3 . The phase diagrams in the space of phenomenological parameters of the LGD potential model with co-dimension (Codim) of 2 and 3, invariant under the cubic point group m3m, were constructed. The values of the phenomenological coefficients of the potential model were determined by fitting experimental data. The theoretical pressure-temperature phase diagram which can explain the experimentally observed cubic-tetragonal-orthorhombic triple point and cubic-orthorhombic phase transition was constructed. Temperature dependences of spontaneous strain, lattice constants, dielectric constants and spontaneous polarization calculated with this potential model were in good agreement with the experimental data. Furthermore, the influence of the hydrostatic pressure on the dielectric constant ( ε 33 ) in the vicinity of the triple point and the dependence of piezoelectric coefficients on the applied electric field were predicted.