An ESR study of hopping conduction in the glass system V2O5-MO2(M=Ge, Se, Te)

X-band ESR spectra of the binary semiconducting glasses 55 mol.% V 2 O 5 -45 mol.% MO 2 (M=Ge, Se, Te) have been examined in the range 298-498K. The three spectra at 298K have distinct differences in their V 4+ resonances which are attributed to a monotonic increase in the covalency of the V-O bond on going from GeO 2 to TeO 2 to SeO 2 . All three compositions show dramatic and reversible temperature dependences by way of the progressive broadening and eventual disappearance of the 51 V (I= 7 / 2 ) hyperfine structure. This behaviour has been attributed to a thermally activated delocalisation of the 3d 1 electron spin leading to hopping electronic conduction.