Pressure and temperature dependence of dielectric properties of cadmium niobate

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Abstract
The pressure (0-7 kbar) and temperature (-180 degrees C to -20 degrees C) dependence of the dielectric properties (complex permittivity, spontaneous polarisation and relaxation) of ceramic Cd2Nb2O7 were investigated. With increasing pressure p the following effects were observed. (1) The improper ferroelectric transition temperature Ti increases with a pressure coefficient dTi/dp approximately=0.4 degrees C kbar-1, and the proper ferroelectric transition temperature Tc, and another transition temperature Ts (Tcsi) indicated by an inflection of permittivity, decrease with pressure coefficients dTc/dp approximately=-1.2 degrees C kbar-1 and dTs/dp approximately=-1.0 degrees C kbar-1, respectively. (2) The permittivities at Ti and Tc decrease rapidly. (3) The shape of permittivity at Ti changes from a kink to a peak. (4) The spontaneous polarisation decreases slightly. The DC bias field effect on the permittivity under pressure is presented. The complex permittivity for the relaxation below Tc under pressure is approximated by the Cole-Cole dispersion law, with the distribution width of the relaxation time being about 0.55. The dielectric relaxation below Tc is of the polydispersion type.