Thermistor behaviour and electric conduction analysis of Ni-doped niobate ferroelectric: the role of multiple β parameters
Résumé
A new engineered non-stoichiometric niobate ceramic with a tetragonal tungsten bronze (TTB)-type structure is prepared by non-isovalent substitution at the niobium backbone. The compound's formula is KSr2(Ni0.75Nb4.25)O15−δ, with space group equal to P4bm (#100), a polar group. Electrical properties of this new ferroelectric-semiconductor ceramic are investigated by impedance spectroscopy in the temperature range from 453 up to 953 K. The curve of the resistance as a function of temperature presents further characteristics of a temperature sensor with a negative temperature coefficient (NTC). At high temperatures, the analysis of electrical parameters shows an NTC behaviour ceramic with three distinct thermistor characteristic parameters, β. The values of the β parameter change from 9.82 × 103 to 1.29 × 104 K, while the temperature coefficient of resistance α changes from −0.047 to −0.023 K−1. The NTC behaviour of KSr2(Ni0.75Nb4.25)O15−δ is compared with the behaviour of some dielectric and other ferroelectric semiconductors. β dependence with dc or the ac conductivity mechanism and its correlation with β quality are discussed.