Structural changes in V₂O₅-P₂O₅ glasses: non-constant force field molecular dynamics and IR spectroscopy

Abstract

Quasi-binary phosphate-vanadate glasses have been studied by both IR spectroscopy and a novel method of molecular dynamics with a non-constant force field. This method is used for the self-assembly of structural models of glasses. The obtained models and the glass network structure are analyzed quantitatively using element distribution by the number of R–O–R bonds (R is phosphorous or vanadium) and 4-, 6-, and 8-membered cycles. The bends on the concentration dependences of atoms distribution in the second coordination sphere agree well with changing the shape of IR spectra. Based on the cycle analysis, the formation of cycles is shown to be more characteristic for vanadate fragments that can form 4-membered cycles, which, according to Zachariasen’s rule, negatively affects glass-forming ability.

Structure–polaronic conductivity relationship in vanadate–phosphate glasses

“…Also, bands below 500 cm −1 belong to the bending vibrations of the phosphate network. On the other hand, a strong narrow band at 1029 cm −1 corresponds to the stretching vibration of short terminal V═O bonds in VO 5 square pyramids, whereas a less intense band at ∼870 cm −1 is related to the stretching of O–V–O bonds in vanadate units 14,31,33,34 . The broad Raman bands at ∼630 and ∼790 cm −1 could be associated with vibrations of both phosphate and vanadate units.…”

“…On the other hand, a strong narrow band at 1029 cm −1 corresponds to the stretching vibration of short terminal V═O bonds in VO 5 square pyramids, whereas a less intense band at ∼870 cm −1 is related to the stretching of O-V-O bonds in vanadate units. 14,31,33,34 The broad Raman bands at ∼630 and ∼790 cm −1 could be associated with vibrations of both phosphate and vanadate units. That is, the band at ∼630 cm −1 could primarily be related to the stretching vibrations of the P-O-P bonds in metaphosphate Q 2 chains 32 but also to the stretching of the P-O-V bonds in mixed vanadate-phosphate units, 23,31,35 whereas the band at ∼790 cm −1 could be assigned to the P-O-P bonds in pyrophosphate Q 1 units 32 as well as to the stretching of the bridging oxygens in V-O-V bonds in mutually connected vanadate units.…”

“…Phosphate glasses containing V 2 O 5 belong to the most investigated family of electronically conducting oxide glasses with a long history of research. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Nearly six decades ago, Denton et al 1 investigated glass-forming properties of the mixture of V 2 O 5 and oxides such as P 2 O 5 , TeO 2 , and BaO, and reported that the obtained glasses exhibit semiconducting properties. The studies that followed showed that oxide glasses containing other transition metal (TM) oxides such as WO 3 , MoO 3 , and Fe 2 O 3 also show electronic conductivity.…”

“…The reason for this most probably lies in the structural complexity of vanadate-phosphate glasses. Indeed, the structure of vanadate-phosphate glasses has been studied by X-ray and neutron diffraction techniques, 10,11,13 vibrational spectroscopies, 14,22,23 and nuclear magnetic resonance (NMR) technique, 24,25 and all these studies have shown the presence of a wide variety of vanadate units from VO 6 distorted octahedra, VO 5+1 square pyramid to VO 4+1 square pyramid and VO 4+1 trigonal bipyramid, with their fractions being dependent on the glass composition. Such complex structural features inevitably have implications on the formation of polarons and their hopping in these materials.…”

“…Phosphate glasses containing V 2 O 5 belong to the most investigated family of electronically conducting oxide glasses with a long history of research 1–14 . Nearly six decades ago, Denton et al 1 .…”