Electrical conduction in copper phosphate glasses containing nickel or cobalt

A variation in d.c. conductivity and activation energy of 35 mol%CuO-65mol%P₂O₅ glasses is observed as CuO is gradually replaced by NiO or CoO. These results are believed to be due to the change in the redox ratio of the two transition metal oxide glasses, which causes an increase and then a decrease of polaron hopping transitions between the ions of the same element and between the ions of the different transition metal elements.     

Effect of cobalt oxide on the a.c. conduction mechanism of copper tellurite glasses

Electrical measurements on binary and ternary glasses of compositions 65TeO₂-35CuO and 65TeO₂-34CuO-1CoO (mol%) are reported at temperatures between 293–458 K in the frequency range up to 10^–6 Hz. The measured conductivity shows a frequency dependence obeying the equation () =A ^s withs <1 but taking different values at different temperatures. The capacitance of the glasses shows an increase in value with increase in temperature at low frequencies. The tangent of the loss angle (tan ) and dielectric loss factor _r were found to increase with the increase in temperature and decrease in frequency but the usual Debye loss peaks were absent even at high temperatures. The relative dielectric constant _r was unexpectedly high, approximately 10³, and was found to decrease very slightly with increasing frequency. Overall the effect of a small amount of CoO (ã 1 mol%) is found to have a dominant effect on the dielectric properties of copper tellurite glasses.     

Comparative study of the effect of the incorporation of cobalt and nickel oxides on the density and optical properties of copper tellurite glasses

Two series of ternary semiconducting glasses with composition 65 TeO₂-(35–x)CuO-xMO in mole percent (x=0, 0.5, 1, 2, 3, 4 and M stands for Co or Ni) were prepared by a melt quenching technique. The densities of annealed and unannealed disc-shaped samples and the optical energy gap of thin blown films of both series of glasses were measured, and the comparative effect of each transition metal (TM) oxide was estimated. It was found that forx=0.5 to 1 mol% andx=2 to 4mol%, the optical energy gap (E _opt) was somewhat greater in TeO₂-CuO-NiO than in TeO₂-CuO-CoO glasses. This increase inE _opt is interpreted in terms of the decreasing number of non-bridging oxygen ions with the increase of each TM oxide. NiO was found to be more effective in increasing the density than CoO in annealed copper tellurite glasses.     

Chemical approach to the conduction mechanism in copper tellurite glasses containing lutetium oxide

Measurements of d.c. electrical conductivity were made on 65TeO₂-(35 -x)CuO-xLu₂O₃ (mol%) glasses with x=0, 1, 2, 3, 4. The experimental results show that whenx is changed from 1 to 2 mol%, the conductivity increases due to the additional electrons obtained by the oxidation of TeO₂ as well as due to the Cu⁺ Cu²⁺ transition under the effect of interelectronic repulsion in the 4f shell of the lutetium present in the glass. Whenx is increased to greater than 2 mol%, the conductivity decreases because hopping is inhibited due to the formation of oxygen bridge associates or because of the strong ligand repulsive field of lutetium indicating its non-reactivity in the glassy network. The conductivity has a distinct maximum atx=2.     

Structural and electronic properties of tellurite glasses

The structural properties of some tellurite glasses were investigated by FT-IR spectroscopy, density measurements, and quantum chemical calculations. Main results reveal that the ratio TeO₄/TeO₃ is found to decrease in the order V₂O₅ > B₂O₃ > P₂O₅. For borate–tellurate glasses, the Van Hove singularities corresponding to Te 5s orbital-derived states are cleft suggesting that there are strong tellurium–oxygen interactions. On the other hand, a strong effect of TeO₂ on the vitreous B₂O₃ network is also demonstrated by FT-IR spectrum. This effect yields the apparition of small peaks in the region ranges between 800 and 1600 cm⁻¹ and probably the partial crystallization of the sample. Its spectral features are due to the B–O bond stretching of [BO₄] and [BO₃] structural units. The quantum chemical data obtained by us show that phosphate–tellurite and vanado–tellurate glasses can behave as semiconductors, whereas borate–tellurite glasses as insulators because the gap between the valence and conduction bands is >3 eV.     

Electrical and magnetic properties of copper tellurite glasses

The glasses of composition (100 − x)TeO₂–xCuO (x = 10, 20, 30, 40, 50 mol%) were prepared by melt quenching method. Differential Scanning Calorimetry (DSC), DC conductivity, Electron Spin Resonance (ESR), and magnetization measurements were undertaken on the glass samples. The glass-transition temperature, T _g, decreases and the thermal stability (ΔT = T _o − T _g) increases with the increase in CuO content. The electrical conduction in these glasses is due to polaron hopping mechanism in the adiabatic regime. The ESR spectra of the x = 10 glass consists of a broad symmetrical line characteristic of Cu²⁺ clusters. The ESR signal linewidth increases and intensity decreases drastically with increase in CuO content from 10 to 20 mol%. No ESR signal could be observed for the glass samples with x ≥ 40. The absence of EPR signal is ascribed to antiferromagnetic interactions between the Cu²⁺ clusters. The magnetization measurements indicate all the samples to be in paramagnetic state. The M–H plots show a small hysteresis loop in the low-field region. These studies indicate the coexistence of antiferromagnetic (AFM) as well as ferromagnetic (FM) interactions between Cu ²⁺ ions in these glasses. The significant change in the properties of the glass at x = 20 is ascribed to the structural changes caused by CuO in the glass matrix.     

Electron spin resonance in copper phosphate and copper tellurite glasses containing strontium

Two series of ternary copper phosphate and copper tellurite glasses containing strontium were prepared and the electron spin resonance spectra of glasses of compositions 65 (P₂O₅)-(35-x) CuO-xSrO and 65 (TeO₂)-(35-x) CuO-xSrO where x varied from 0–10 mol % were investigated. From the results and the chemical analyses of the samples it was found that a reduction in the copper (II) signal intensity in the glass samples as the proportion of alkaline earth metal is raised, corresponds to an increase in the reduced valency ratio, C, in the glasses.     

Control of electrical conductivity with the admixture of chlorine in copper tellurite glasses

Copper tellurite glasses containing. CuCI₂ with composition 65TeO₂-(35–x)CuO-xCuCl₂ (mol%) with x=0, 1, 2, 3, 4, 5 were prepared by quenching the melt. An increase in density with the addition of CuCl₂ and with a corresponding decrease in molar volume, has been observed. The d.c. conductivity of copper tellurite glasses is found to be very sensitive to the reduced valency rationC=[Cu⁺]/[Cu_total] and depends on the relative concentrations of Cu⁺ (reduced valency state) and Cu²⁺ (higher valency state) ions. It is found that by adding cupric chloride to the melt when the glass is formed, the chlorine in the salt which acts as an oxidizing agent alters the ratio of the concentrations of Cu⁺ and Cu²⁺ ions in the glass and hence the conductivity. It is found that more than 2 mol% of cupric chloride reduces the conductivity very sharply due to the formation of chlorine clusters in the form of local TeCl₂₊ whereas less than 2 mol% of CuCl₂ leads to an increase in conductivity due to the Cu⁺Cu²⁺ transition which is negligibly affected by the chlorine due to the formation of TeCl₂ which is amorphous in nature. The increase and decrease of electrical conductivity of glasses containing less or more than 2 mol% CuCl₂ is also interpreted in terms of the electronic transitions between the orbitals of tellurium 3d electrons, their binding energies and peak widths on the basis of XPS (X-ray Photoelectron Spectroscopy) study, and it was found that the increase in bandwidth supports the idea of clustering of chlorine above 2 mol% CuCl₂ and causing a decrease in the conductivity. Overall the conductivity is found to be somewhat uncontrollable in these glasses because it is not simply dependent on the concentration of Cu²⁺ ions.     

Devitrification and vitrification of tellurite glasses

The crystallization of pure tellurite glass during various heating rates was studied. The activation energy for crystallization was 115 × 10²² eV mol^–1. The glass transformation, T _g, starting crystallization, T _x, crystallization, T _c and melting temperatures, T _m, have been reported for binary tellurite glasses of the form (1 – x) TeO₂–xA_nO_m [A_nO_m = MnO₂, Co₃O₄ and MoO₃]. Among many different parameters of the glass forming potential the two-thirds rule, T _g/T _m, the glass stabilization range, T= T _x – T _g, and the glass forming tendency, K _g= (T _c– T _g)/(T _m – T _c), are reported for the first time for tellurite glasses.     

Nano-network electronic conduction in iron and nickel olivine phosphates

The provision of efficient electron and ion transport is a critical issue in an exciting new group of materials based on lithium metal phosphates that are important as cathodes for lithium-ion batteries. Much interest centres on olivine-type LiFePO(4), the most prominent member of this family. Whereas the one-dimensional lithium-ion mobility in this framework is high, the electronically insulating phosphate groups that benefit the voltage also isolate the redox centres within the lattice. The pristine compound is a very poor conductor (sigma approximately 10(-9) S cm(-1)), thus limiting its electrochemical response. One approach to overcome this is to include conductive phases, increasing its capacity to near-theoretical values. There have also been attempts to alter the inherent conductivity of the lattice by doping it with a supervalent ion. Compositions were reported to be black p-type semiconductors with conductivities of approximately 10(-2) S cm(-1) arising from minority Fe(3+) hole carriers. Our results for doped (and undoped) LiMPO(4) (M = Fe, Ni) show that a percolating nano-network of metal-rich phosphides are responsible for the enhanced conductivity. We believe our demonstration of non-carbonaceous-network grain-boundary conduction to be the first in these materials, and that it holds promise for other insulating phosphates.     

IR spectra and structures of tellurite glasses

It is shown with IR spectral investigations that the short range order of certain tellurite glasses, obtained from monomineral crystalline phases, is similar to that of the crystals. They may contain the following polyhedra: TeO₄-trigonal bipyramids (C_2v symmetry), deformed TeO₄ groups, TeO₃ trigonal pyramids (C_3v point symmetry), or combinations of these polyhedra. The introduction of V₂O₅ and MoO₃ in the binary glasses leads to a TeO₄ → TeO₃ transition. MoO₃ delays the decay of TeO₄ groups in a wider concentration range.     

Carbothermic reduction of copper,nickel, and cobalt oxides and molybdates

The carbothermic reduction of NiO, CoO, CuO, MoO₃, and the MMoO₄ (M = Ni, Co, Cu) molybdates has been studied by thermogravimetry. The results demonstrate that the reactivity of the molybdates with solid carbon, the sequence of reduction reactions, and the composition of reaction intermediates are determined by the reactivity of the constituent oxides, which decreases in the order CuO > MoO₃ > NiO > CoO. The reaction intermediates in the reduction of CuMoO₄ are Cu₆Mo₅O₁₈ and Cu₂Mo₃O₁₀, and those in the reduction of CoMoO₄ are Co₂Mo₃O₈ and CoMoO₃. NiMoO₄ is reduced without oxide intermediates. The reactions of CuMoO₄ and NiMoO₄ with solid carbon lead to selective reduction of the molybdates to metals (Cu or Ni) and molybdenum oxides (MoO₂ and MoO_{3 ? x} ). In the reactions of NiMoO₄ and CoMoO₄ with CO gas, the metals are formed at comparable rates, which favors the formation of metal solid solutions, intermetallic phases, and mixed carbides.     

Dielectric properties and polarizability of molybdenum tellurite glasses

The dielectric behaviour of the [TeO₂]_1–x [MoO₃] _x , x=0.2, 0.3 and 0.45 mol%, glassy system is reported for the temperature range 300–573 K and the frequency range of 0.1–10 kHz. Both the static and high frequency dielectric constants for these binary tellurite glasses decrease with increasing MoO₃ content. The temperature dependence of the dielectric constants of these glasses are positive. The frequency dependence of the dielectric constant identifies a frequency dependence which does not show a flattening at low frequency. The room temperature static dielectric polarizability is discussed in terms of the MoO₃ concentration. The temperature dependence of the dielectric constant has been analysed in terms of the temperature changes of both volume and polarizability and also a volume change of the polarizability.     

碲铌铅玻璃的椭圆偏振光谱研究

折射率,色散和吸收系数是用于超高速全光开关的光学材料的重要品质指数。本文用椭圆偏振仪对碲铌铅（TNP）玻璃试样作波长自动扫描测量,测得在波长λ＝258.3-826.6nm范围内的折射率图谱与消光系数图谱,从而可计算各试样的阿贝数ud和非线性折射率n2,结果表明TNP玻璃具有较高的n2,因此TNP玻璃是可以作为超高速全光开关候选材料之一。     

Direct and alternating electrical conduction in copper phosphate glasses containing praseodymium and calcium

Glasses of various compositions were prepared and included Pr₆O₁₁-CuO-P₂O₅ and Pr₆O₁₁-CaO-CuO-P₂O₅. The direct electrical conduction mechanism was generally discussed in terms of small polarons for the whole series of glasses. Alternating electrical conduction was discussed according to the Elliott model and the Meyer-Neldel rule.     

The effects of copper and iron oxide additions on the sintering and properties of Y-TZP

Yttria-tetragonal zirconia polycrystals (Y-TZP) with a range of yttria contents were prepared from powders neutralized during processing with ammonium hydroxide and sintered at temperatures of 1300–1700 °C. Iron or copper oxide was ádded and studies made of body characteristics, mechanical properties and ageing resistance. Densification was aided by higher yttria concentrations. The effects of the oxide additives were dependent on amounts present and sintering conditions, including ramp rates and holding temperatures. Ageing resistance was significantly improved for both oxide additions fired to lower temperatures but rapid transformation to monoclinic phase was observed for materials with larger grain sizes associated with higher sintering temperatures.