Dielectric properties of Ag_1-<i>x</i>A_<i>x</i>NbO₃(A: K, Na and Li) and AgNb_1-<i>x</i>Ta_<i>x</i>O₃solid solutions in the vicinity of diffuse phase transitions

Abstract

Low-frequency (100 Hz-1 MHz) dielectric studies of the AgNb1-xTaxO3 (ATN) (0⩽x⩽0.4), Ag1-xKxNbO3 (AKN) (0⩽x⩽0.04), Ag1-xLixNbO3 (ALN) (0⩽x⩽0.04) and Ag1-xNaxNbO3 (ANN) (0⩽x⩽0.4) solid solution ceramics were carried out in the temperature range 120-700 K. The dielectric dispersion was only observed within the ferroelectric M1 phase. For all the investigated materials the M1-M2 phase transition exhibits the ferroelectric relaxor-like character. The relations between the frequency and the temperature (Tm) of the maximum dielectric permittivity ε' only obey the Vogel-Fulcher law for the ALN ceramics. Measurements of remanent polarization Pr were performed within the ferroelectric M1 phase. Two different origins of the ferroelectric state are proposed. The possibility that the M1 ferroelectric phase is of ferrielectric nature is also discussed. The diffuse M2-M3 phase transition is frequency independent. These results allowed us to consider the coexistence of the ordered and disordered subsystems in silver niobate and its solid solutions.