Abstract
ABSTRACT Temperature dependences of the order parameters (P and Ψ) and inverse susceptibilities (χp −1 and χΨ -1 ) are calculated for the ferroelectric(FE)-incommensurate (INC) – paraelectric (PE) transitions in NaNO2 at zero (E = 0) and constant electric fields E by the Landau phenomenological model. For the calculation of the polarisation P and the order parameter Ψ, the phase line equations are fitted to the observed data (E = 0) from the literature. On this basis, E-T phase diagram including the ferroelectric, incommensurate and paraelectric phases is constructed using the observed (E-T) data for NaNO2 as reported in the literature. In the presence of the polarisation P (secondary order parameter), which has a biquadratic coupling with the Ψ (primary order parameter) in the incommensurate phase, the Landau model presented here describes the observed behaviour of the FE-INC and INC-PE transitions in NaNO2. Under constant electric fields, our predictions can be compared with the experiments. This method of calculation can be applied to some other crystals exhibiting the incommensurate phase between the FE and PE phases.
Published Version
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