Crystallization of ferroelectric bismuth vanadate in $Bi_2O_3-V_2O_5-SrB_4O_7$ glasses

Transparent glass samples with compositions 2 xBi(2)O(3-x)V(2)O(5)-(100 - 3x)SrB4O7 (15 less than or equal to x less than or equal to 25) have been fabricated via conventional melt-quenching technique. The as-quenched samples, of all the compositions under study, have been confirmed to be amorphous by X-ray powder diffraction (XRD) measurements. Differential thermal analyses of the glasses (x = 20 and 25) indicate a prominent exotherm in the 673 K to 683 K range and the XRD patterns of the samples, obtained by the heat treatment of the glasses at 683 K for 10 h, indicate crystallinity and all the crystalline peaks could be indexed to an orthorhombic ferroelectric bismuth vanadate, Bi2VO5.5 (BiV) phase. High-resolution transmission electron microscopy on these samples confirm the presence of BN crystallites dispersed in a continuous glass matrix. The dielectric properties of these glass-ceramics have been analysed by employing Maxwell's model and various other dielectric mixture formulae. The study of the temperature dependence of epsilon(r) of these glass-ceramics has revealed a dielectric maximum in the vicinity of the temperature at which crystalline BiV has a phase transition from the ferroelectric to paraelectric state. The compositional dependence of the optical properties of these transparent glass-ceramics has also been measure