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.     

Different effects of nickel and cobalt additions on the electronic conduction of copper tellurite glasses

Measurements of the d.c. electrical conductivity were made on 65TeO₂-(35-x)CuO-x(MO) (mol %) glasses wherex=0, 0.5, 1, 2, 3, 4 and M represents nickel or cobalt. A variation in the conductivity and activation energy of the glasses is observed as CuO is replaced by NiO and by CoO. It is found that withx=0.5 to 3 mol % of NiO, the conductivity increases and the activation energy decreases due to the decrease in effective electron hopping distance between the transition metal (TM) ions. The conductivity is found to decrease with the substitution of 4 mol % of NiO and 0.5 to 4 mol % of CoO and this is attributed to the decrease in relative concentration of hopping centres because of the decrease in the hopping transitions between ions of the same element (e.g. Cu⁺ and Cu²⁺ ions) and between the ions of different TM elements (e.g. Cu⁺ and Ni²⁺, Cu⁺ and Co²⁺). This decrease in conductivity has also been described due to the formation of Ni-O-Ni, Cu-O-Ni and Co-O-Co, Cu-O-Co bridge bonds in NiO-and CoO-doped glasses respectively. The CoO-doped glasses have been found to be of a more insulating nature.     

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.     

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.     

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.     

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.     

Further MN rule in thermally activated a.c. conduction of Se-Te-Sb chalcogenide glasses

Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se₇₀Te_30−xSb_x (4 ≤ x ≤ 10) alloys. The observation of Further Meyer-Neldel rule in case of a.c. conductivity is reported. The observation of the correlation between Meyer-Neldel pre-factor σ₀₀ and Meyer-Neldel energy is explained by multiple excitations stimulated by optical phonon energy as described by Yelon and Movaghar.     

D.c. conduction studies on thermally evaporated neodymium oxide thin films

Aluminium-neodymium oxide-aluminium thin film capacitors have been prepared by thermal evaporation and the d.c. conduction properties of these films have been studied. The thicknesses of the films have been determined by a multiple beam interferometer. The current-voltage power-law dependence showed that the conduction in these films is space-charge limited. The linear dependence of the current density on the square root of the applied field confirmed the exponential trap distribution. The trap density has been found to be of the order of 10²⁶ m^–3. It has also been observed that the Schottky type of conduction is predominant in the high-field region and the height of the Schottky barrier has been determined. It is seen that the conduction mechanism is an activated process with the activation energy decreasing with increasing field.     

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。     

Photocurrent enhancement of d.c. sputtered copper oxide thin films

Copper oxide (CuO) thin films with photocurrent as high as 25 μA/cm² were deposited on conductive glass substrates using d.c. reactive sputtering. This was the highest reported photocurrent for sputteredp- type copper oxide measured in the electrolyte KI. The photocurrent drastically increased up to 25 (μA/cm² as the sputtering pressure and the substrate temperature were increased up to 8.5 mbar and 192°C, respectively. All the synthesized films contained single phase of CuO in this range of pressure and substrate temperature. Variation of the photocurrent, photovoltage, structure and absorbance with deposition conditions were studied in detail.     

Effect of cobalt oxide on the densification of yttrium aluminum garnet

The solid state sintering of yttrium aluminum garnet (YAG) without any additive at 1873 K could not be achieved beyond 90% of theoretical density. Higher temperature was not tried to avoid abnormal grain growth in the material. To densify further, cobalt nitrate was added to alumina–yttria stoichiometric mixture in various proportion by solution infiltration method. The samples were sintered at 1873 K in air to achieve full density. The as-sintered microstructure revealed no abnormal grain growth.     

Explanation of Meyer–Neldel rule in the thermally activated a.c. conduction in some chalcogenide glasses using correlated barrier hopping model

We have investigated Meyer–Neldel rule in thermally activated a.c. conduction for a-Se₈₀Te₂₀ and a-Se₈₀Te₁₀M₁₀ (M = Cd, In, Sb) alloys by two different approaches. In the first case, the temperature dependence of a.c. conductivity is studied at different audio frequencies without changing the composition of glassy system. In the second case, the composition itself varies at a particular audio frequency. The results are explained by using well-known correlated barrier hopping model.     

Mixed mobile ion effect on a.c. conductivity of boroarsenate glasses

In this article we report the study of mixed mobile ion effect (MMIE) in boroarsenate glasses. DSC and a.c. electrical conductivity studies have been carried out for $\boldsymbol{x}$ MgO?C(25 $\boldsymbol{-}$ $\boldsymbol{x}$ )Li ₂ O?C50B ₂ O ₃ ?C25As ₂ O ₃ glasses. It is observed that strength of MMIE in a.c. conductivity is less pronounced with increase in temperature and frequency. The results were explained on the basis of structural model (SM) proposed by Swenson and his co-workers supporting molecular dynamic results.     

The a.c. conductivity of CuO-containing lead silicate glasses

The a.c. conductivity of copper-free and copper-containing lead silicate glasses of the base composition 80PbO–20SiO₂ (wt %), equivalent to 51.5PbO–48.5SiO₂ (mol %), was measured at different temperatures and frequencies. The ratio Cu²⁺/Cu_total as a function of CuO content in the glasses studied was quantitatively determined by ESR. The results were used to derive the mechanism of conduction in lead silicate glasses. Values of a.c. conductivity, dielectric loss and dielectric constant decreased with the addition of CuO up to 0.25 g/100 g glass and increased with further additions of CuO. This may be due to the gradual decrease in the ratio Cu²⁺/Cu_total (as indicated by ESR) with increasing CuO content, through reduction of some Cu²⁺ ions to Cu⁺ ions, which have higher mobility. The a.c. conductivities agreed with the Anderson and Stuart model and indicated that the conduction mechanism was ionic in character.     

D.c. and a.c. conduction in amorphous titanium dioxide thin films

The d.c. and a.c. measurements were performed with two groups of vacuum- deposited amorphous TiO₂ thin films which had metal-TiO₂-metal sandwich structures. The d.c. conduction process and the frequency dependence of the a.c. conductivity σ_ac of “group 1” samples,which contained numerous oxygen vacancies, showed the three-dimensional Poole-Frenkel effect and σ_ac was proportional to the frequency ? over the range 50 Hz–50 kHz. “Group 2” samples, in which the vacancies were subsequently removed by heat treatment in air, showed the three-dimensional anomalous Poole-Frenkel effect and σ_ac was proportional to ?ⁿ where n was 0.7–0.8.     

The effects of the incorporation of lutetium oxide on the density and optical properties of copper phosphate glasses

A range of phosphate glasses containing lutetium was prepared by the melt quenching technique. The densities of annealed and unannealed glass samples, molar volumes and the optical energy gapE _opt of thin blown films of the glasses were determined. It was found that the density and molar volume both increased with increase of Lu₂O₃ content. TheE _opt values showed that they are not sensitive to the incorporation of small amounts of oxides.