Zależność między szerokością pasma wzbronionego a temperaturą Curie w ferroelektrycznych roztworach stałych ze strukturą typu perowskitu

Abstract

On the base of the spectral dependence of the photoconductivity the width of forbidden band E[g] was determined in ferroelectric solid solutions: x PbTiO[3] – (1-x)SrTiO[3] I, x PbTiO[3] – (1-x)PbZrO[3] II, AgNbO[3] – (1-x)NaNbO[3] III, x PbTiO[3] – (1-x) NaNbO[3] IV. It was found, that for the solid solution of type I the dependence T[c] = T[c](0) – αE[g] takes place arising from the interband theory of ferroelectricity; T[c](0) = 68*10[2]K, α= 0.176, T[c] – Curie temperature. For other solid solutions (II, III and IV) this dependence does not take place, but for II and III the dependence T[cw] = T[cw(0)] – αE[g], takes place where T[cw] is the Curie-Weiss temperature. The experimental values for II are: T[cw(0)] = 24,2 x 10[2]K, α = 0.049, and for III – T[cw(0)] = 8.5 x 10[2]K, α = 0.0115. It has been concluded that the linear dependence between E[g] and T[c] (T[cw]) takes place only in ferro and antiferroelectric solid solutions where both components belong to the same type (A[2+]B[4+]O[3] or A[1+]+B[5+]O[3]).