High-temperature phase transitions in a quaternary lead based perovskite structured materials with negative temperature coefficient of resistance (NTCR) behavior

摘要

Impedance spectroscopy measurements were carried out on lead based, 0.25 (PbZr_(0.52)Ti_(0.48)O_3) + 0.25 (PbFe_(0.50)Ta_(0.50)O_3) + 0.25 (PbFe_(0.67)W_(0.33)O_3) + 0.25 (Pb Fe_(0.50)Nb_(0.50)O_3) (PZT-PFT-PFW-PFN) solid solution over a wide range of temperatures (400-650 K) and frequencies (100 Hz-1 MHz). Impedance data showed the presence of both grains and grain boundaries effects in the electrical transport properties of quaternary. The role of the grains and grain boundaries to the impedance become more prominent around the phase transition (～420 K). Two thermally activated processes were found from the temperature dependences of the relaxation time (τ). Activation energies calculated from relaxation times obtained from imaginary part of impedance were estimated ～1.21 and ～ 1.84 eV over 400-490 K and 490-650 K respectively. The sum of the activation energies for the grain and grain boundary resistances is basically of the same order of magnitude that is from the impedance at high temperatures. A constant phase element is used in the equivalent electrical circuits for fitting of experimental impedance data. The nature of variation of the grain and grain boundary resistance with temperature suggested negative temperature coefficient of resistance behavior.