Molybdenum Phosphate Research Articles

Composition dependence of the infrared absorption spectra of molybdenum phosphate glasses and some crystalline analogues

The infrared spectra of the entire glass-forming range of the vitreous system Mo-P-O are reported. The data are interpreted in the light of previous studies of other vitreous phosphates, and related crystalline phosphates. The spectra show that with increasing MoO 3 content progressive rupture of P = O bonds takes place and there is little of the bond-type left in compositions exceeding 53 mol% MoO 3 . The P=88O stretching frequency is reduced by hydrogen bonding but increases with increasing Mo content. The P-O-P ring frequency is strong throughout most of the composition range, consistent with a three-dimensional network structure relatively free of chains. The spectra in midcomposition range are characterised by vibrations characteristic of PO 3 and P 2 O 7 groups with edge sharing MoO 6 octahedra having relatively little effect. However, the spectra of Morich structures display unique features characteristic of edge sharing MoO 6 octahedra as in pure MoO 3 oxide. Generally, the data are also consistent with the proposition, used in a previous ultrasonic study, that these glasses consist of distorted versions of the crystal groups: PO 4 tetrahedra, MoO 3 octahedra, metaphosphate and pyrophosphate, in proportions that change systematically and distinctively with content. It is suggested that acoustic and optical Debye temperatures calculated from these spectra ought to correlate with (in respect of composition dependence) analogous quantities calculated from published data on acoustic wave velocities and the temperature dependence of electrical conductivity in this wide-ranging glass system.

Microwave measurement of the temperature dependence of permittivity in molybdenum phosphate glasses

Etude de l'effet de la temperature sur la permittivite et la perte dielectrique a 35 GHz de verres MoO 3 -P 2 O 5

The polymerization of hexachloro cyclotriphosphazene by molybdenum phosphate and tungsten phosphate

AbstractThe polymer of (NPCl2)3 was obtained by bulk polymerization. Especially, linear polymer was predominantly formed when tungsten phosphate as catalyst was used.

A study of the electrical properties of molybdenum phosphate glasses

A series of binary MoO3-P2O5 and also ternary MoO3-P2O5-In2O3 glasses were prepared and their electrical properties were investigated. The d.c. conductivity measurements show that the conduction in molybdenum phosphate glasses is by a hopping process in which the electrical charge transfers from Mo5+ to Mo6+ ion sites. The conductivity can be discussed in terms of the small polaron conduction mechanism. In contrast to vanadium phosphate glasses, the tunnelling term in the conductivity formula seems to make a significant contribution in molybdenum phosphate glasses and is associated with a hopping process in the non-adiabatic regime.

A molybdenum(IV) phosphate with a tunnel structure TlMo2P3O12

A molybdenum(IV) phosphate with a tunnel structure TlMo₂P₃O₁₂

Thermoelectric power in transition metal oxide glasses

The thermoelectric power in different compositions of WO3-P2O5, V2O5-P2O5 and MoO3-P2O5 has been measured in the temperature range 150 to 400K for tungsten and vanadium phosphate glasses and 300 to 450K for molybdenum glasses. Heikes' formula for the thermal power and the small polaron model can adequately explain the experimental results in tungsten and vanadium phosphate glasses. However, the contribution of alpha (heat of transport associated with kinetic energy) in Heikes' formula cannot be ignored. Molybdenum phosphate glasses give an extremely low value of thermal power ( approximately 10 mu V K-1) and the measured values cannot be explained by Heikes' formula.

DC conductivity of molybdenum phosphate glasses

The temperature dependence of DC conductivity in the high-temperature range in transition metal oxide glasses containing MoO3, WO3 and V2O5 is presented. Molybdenum phosphate glass has been investigated with MoO3 contents varying from 60 to 85 mol% while vanadium and tungsten phosphate glasses have been examined for one composition only. The conductivity of a molybdenum phosphate glass is considerably lower than that of tungsten and vanadium phosphate glasses of similar composition while the activation energy is higher for the molybdenum glass. The DC conduction in molybdenum phosphate glasses can be considered to be due to hopping of polarons and is consistent with the reported results of other transition metal ion phosphate glasses.

Dielectric dispersion in molybdenum phosphate glasses

Dielectric measurements for an 85 mol.% MoO3-15 mol.% P2O5 glass sample have been made from 77K to 475K at four fixed frequencies 0.1 kHz, 1 kHz, 10 kHz and 100 kHz. It has been observed that a Debye-type dielectric relaxation exists in the temperature region where AC conductivity at a given frequency approaches DC conductivity. A distribution of relaxation times is needed to explain the relaxation behaviour; however, the value of the distribution parameters is much smaller than that required to account for the almost linear dependence of conductivity on frequency. A comparison with vanadate glasses shows that the numerical magnitude of the Cole-Cole distribution parameter is almost the same for both the systems.

Electrically Conducting Glass Fibers

Fiber formation and electrical conductivity were investigated in molybdenum phosphate glasses containing Ag2O; PdO was substituted for Ag2O and other constituents in the base glass. Temperature coefficients of electrical resistivity and linear expansion and other properties were determined for the bulk glasses. X-ray diffraction confirmed that some compositions were amorphous; these glasses could be drawn by conventional methods into continuous filaments. Migration and reduction of Ag+ at the glass fiber surfaces, induced by a secondary heat treatment, formed a metallic, electrically conducting, solder-able surface film. Filament resistance of 0.07 Ω/ft/2000 fibers was achieved; resistance increased nearly linearly with temperature from −200° to 200°C. Imperfections in the metallic film, acting as flaw sites, contributed to a reduction of ∼50% in tensile strength compared to that of pristine fibers.