Dielectric properties of Ag1-xAxNbO3 (A: K, Na and Li) and AgNb1-xTaxO3 solid solutions in the vicinity of diffuse phase transitions

Low-frequency (100 Hz-1 MHz) dielectric studies of the AgNb1-xTaxO3 (ATN) (0 less than or equal to x less than or equal to 0.4), Ag1-xKxNbO3 (AKN) (0 less than or equal to x less than or equal to 0.04), Ag1-xLixNbO3 (ALN) (0 less than or equal to x less than or equal to 0.04) and Ag1-x,NaxNbO3 (ANN) (0 less than or equal to x less than or equal to 0.4) solid solution ceramics were carried out in the temperature range 120-700 K. The dielectric dispersion was only observed within the ferroelectric M-1 phase. For all the investigated materials the M-1-M-2 phase transition exhibits the ferroelectric relaxer-like character. The relations between the frequency and the temperature (T-m) of the maximum dielectric permittivity epsilon ' only obey the Vogel-Fulcher law for the ALN ceramics. Measurements of remanent polarization P-r were performed within the ferroelectric M-1 phase. Two different origins of the ferroelectric state are proposed. The possibility that the M-1 ferroelectric phase is of ferrielectric nature is also discussed. The diffuse M-2-M-3 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.