X-ray diffraction, density and electrical conductivity studies of some zinc borate glasses

Abstract

The behaviour of electrons in glasses has been a subject of growing interest for more than two Specimen decades. It was Baynton et al. [1] who laid the foundation for such interest but later on many papers [2-8] have been published on electrical a and other physical properties of chalcogenide and b transition metal oxide glasses. The concept of c localization introduced by Anderson [9] and the d principle of Ioff6 and Regel [10] are crucial for e our present understanding of non-crystalline materials in modern terms. It was first proposed by Gubanov [11] that the electronic states are localized near the edges of conduction or valence bands in most non-crystalline materials and then Mott [5] pointed out for the first time that if the states are localized throughout the band there must exist an energy E e separating localized and non-localized states. As the electrical conductivity is affected by the electronic states present in the band gap, different models [8] have been proposed to describe the conduction mechanism in non-crystalline materials. Generally this is based on hopping between localized states and 3.9 the expression given by Mott for d.c. electrical conductivity based on a multi-range hopping conduction model is currently receiving much 33 attention. The present work is a part of the "~ 3.5 research programme of this laboratory aimed at an understanding of the properties of oxide glasses of potential interest in the electronics field. ~ 3.3 Analytical reagent grades of ZnO and B2Os were used in which the B2Oa was 99.999% pure. 3.1 Glasses were prepared in alumina crucibles at l l00°C and annealed at 500°C. The X-ray 2.9 diffraction patterns were recorded with a DebyeScherrer camera using nickel-filtered CuKa 2.7 radiation and showed diffuse haloes, characteristic of glassy materials. Tile densities were measured by the displacement method using toluene as an immersion liquid. All the glass compositions, their