JOURNAL OF MATERIALS SCIENCE LETTERS 1 (1982) 264--267 Internal friction and electrical conductivity in iron--vanadium--phosphate glasses W. CHOMKA, O. GZOWSKI, L. MURAWSKI, D. SAMATOWlCZ Institute of Physics, Technical University Gdaf}sk-Wrzeszcz, Majakowskiego 11/12, Poland S. STIZZA, I. DAVOLI, V. PRANTERA Instituto dl Fisica, Universita di Camerino, Camerino, Italy It is a well recognized fact that the electrical con- ductivity in transition metal oxide glasses is due to the existence of ions in different valency states and the hopping of the electrons between these ions [1-3]. In recent years, investigations have been reported [4-6] on internal friction and electrical properties of these glasses. The internal friction peak as well as the dielectric loss peak were interpreted as the result of dipole re-orientation under the electric field or mechanical stress. In the iron-phosphate glasses the jump of the electron from the bivalent to the trivalent iron ion produces such a re-orientation of both the elec- trical and elastic dipoles. A similar effect can be expected when glass contains two different transition metal oxides, e.g. iron and vanadium. In this case, one may expect, apart from the transition Fe 2÷ ~ Fe 3÷, the transition V ++ ~ V s+ and also the Fe 2÷ ~ V s+ or V+++ Fe 3+ transitions. We have briefly reported the results of electrical conductivity [7] and internal friction [8] of phosphate glasses con- taining up to 50mo1% of V+Os and FeO. Since it is impossible to obtain the redox ratio, C, of both transition metal elements directly by chemi- cal analysis, M6ssbauer spectroscopy studies were conducted in order to determine the valency state of iron ions [7]. However the valency state of vanadium ions was still unknown and the full interpretation of conductivity and internal friction results was impossible. Recently, we have con- ducted some experiments using the method of X-ray absorption near edge structures (XANES) for determining the local site symmetry of vanadium ions [9]. These measurements will be fully reported later, but some results concerning the valency state of vanadium ions will be used in order to explain the internal friction and conductivity results. Glasses of composition 50mo1% P2Os+ (50--x)mol% FeO +xmol% V2Os and 50mo1% P2Os + (50--x)mol% CaO +xmol% V2Os were melted in an air atmosphere in alumina crucibles at 1500K for 3h. They were made from the reagent-grade materials V2Os, Fe2Oa, CaO and NH4H~PO4. The measurements of electrical conductivity of the button-shaped samples by a three-terminal method were carried out in vacuum. The measurements of the internal friction, Q-', of the fibre samples were performed with a torsion pendulum in the frequency range 1 to 34 Hz and at temperatures between 150 and 600 K. Fig. 1 presents a typical set of the electrical conductivity temperature characteristics for six glasses of different compositions. The character- istics in high temperature regions are well described by the equation o = Oo exp (--E/kT) where E is the activation energy, k is the Boltzmann constant and T is the temperature. The minimum of the conductivity and the maximum of activation energy is observed for 10 real% of V205. Fig. 2 presents the set of internal friction results. Only the low temperature peaks, which are typical for the electron transition, are shown. For 5 to 10 percent V2Os content, a splitting of the peak is observable. The arrows indicate the position of the peak when only iron is present in the glass matrix [10] and instead ofV2Os, CaO in the same percentage is added. For the sake of com- parison, Fig. 3 shows the internal friction results for vanadium glasses, where instead of iron, the neutral modifier CaO is introduced. In iron phosphate or vanadium phosphate glasses, there exists a mixed valency system of iron or vanadium ions and the value of the conduc- tivity depends on the amount of transition metal 264 0261-8028/82/060264-04502.98/0 © 1982 Chapman and Hall Ltd.