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- Title
Investigation of Spontaneous Polarization and Phase Transition Phenomena in KH<sub>2</sub>PO<sub>4</sub>-Type Crystals by Green's Function Approach.
- Authors
Kumar, Kuldeep; Upadhyay, Trilok Chandra
- Abstract
In this paper, the spontaneous polarization and the phase transition of order–disorder type H-bonded KH2PO4-type crystals are theoretically investigated. With the help of a modified (presently) model Hamiltonian, and by applying the double-time thermal-dependent statistical Green's function technique and Dyson's equation, various expressions are derived for KH2PO4-type crystals. In this (PLCM) model, the direct spin–spin interaction term, the four-body interaction term, extra spin–phonon interaction term, and the third-order and fourth-order lattice anharmonic interactions terms are considered. Theoretical expressions for the spontaneous polarization, Cochran's soft-mode frequency, energy shift and width, permittivity, and tangent delta (tanδ) are derived. Thermal variations for these quantities with temperature are found. The formulae for these quantities are derived by using Green's function method. Model values are fitted for a KH2PO4 crystal to obtain the variation with temperature. The results are compared with experimental variations reported by other workers (Kaminow and Damen, Phys Rev Lett 20(20):1105, 1968; Von and Bantle, Helv Phys Acta 17:298–318, 1944). A good agreement is observed.
- Subjects
GREEN'S functions; PHASE transitions; SPIN-spin interactions; ORDER-disorder transitions; CRYSTALS; FERROELECTRIC liquid crystals
- Publication
Journal of Low Temperature Physics, 2022, Vol 207, Issue 3/4, p190
- ISSN
0022-2291
- Publication type
Article
- DOI
10.1007/s10909-022-02714-y