Composition dependence of the ferroelectric-paraelectric transition in the mixed system ${\mathrm{PbZr}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ti}}_{\mathit{x}}$${\mathrm{O}}_3$

The dielectric constant and losses of good quality ceramic samples of Nb-doped (1 wt % ${\mathrm{Nb}}_2$ ${\mathrm{O}}_5$) ${\mathrm{PbZr}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ti}}_{\mathit{x}}$ ${\mathrm{O}}_3$ about the ferroelectric-paraelectric transition for 0.03≤x≤0.09 have been measured with the aim of investigating the behavior of the thermal hysteresis with composition and the possible existence of tricritical points in this mixed system. The trend of the data, analyzed in terms of a generalized effective-field theory (${\mathit{E}}_{\mathrm{eff}}$=E+βP+γ${\mathit{P}}^3$+...) indicates that two tricritical points, at x≃0.26 and x≃0.51, are implied by the observed behavior at lower x.