Some physical properties of V2O5-Fe2O3 and V2O5-Fe2O3-Li2O systems

Various methods have been used to study the physical properties of the V₂O₅-Fe₂O₃ and V₂O₅-Fe₂O₃-Li₂O systems, including X-ray, electron microscope, Mössbauer effect, NMR and thermogravimetric measurements. The iron ions are approximately equally distributed in substitutional and interstitial sites in the V₂O₅ lattice. The maximum number of iron ions dissolved in the V₂O₅ matrix corresponds to 4 mol % Fe₂O₃. In all the samples a quantity of Fe₂O₃ which has not been included in lattice is observed. The V₂O₅-Fe₂O₃ and V₂O₅-Fe₂O₃-Li₂O systems are formed from solid solutions mixed with very small Fe₂O₃ particles. The analysis of the charge compensation of iron ions suggests that V₂O₅ is a quasi-amorphous semiconductor. Irradiation of V₂O₅-based samples with an electron beam induces the V₂O₅ platelets to convert to the VO _x phase.     

X-ray photoelectron spectroscopic studies of evaporated V2O2and co-evaporated V2O5/B2O3 films

X-ray photoelectron spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been investigated. The photoelectron spectrum of a simple V₂O₅ film shows the splitting of the V 2p level in accordance with the spins. The values of binding energies corresponding to V 2p and O1s are comparable with those reported previously. For co-evaporated V₂O₅/B₂O₃ films a chemical shift in the O 1s level has been observed which has been attributed to the changed chemical environment of oxygen as a result of the presence of boron and vanadium atoms. The values of binding energies for V 2p_3/2 and O 1s corresponding to simple evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ show the presence of V₂O₄ species in the films.     

Optical absorption studies for TeO2-P2O5 and Bi2O3-TeO2-P2O5 glasses

A range of TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ glass systems were prepared. The optical absorption spectra were measured in the spectral range 300–800 nm and it was found that the fundamental absorption of these glasses is dependent on the glass composition. The optical energy gap of binary glasses increases with increasing TeO₂ content while the addition of Bi₂O₃ to TeO₂-P₂O₅ decreases the optical energy gap. The absorption edges of these glasses arise from direct forbidden transitions and occur at photon energies in the range of 2.17 to 2.97 eV for TeO₂-P₂O₅ glasses and 2.63 to 2.32 eV for Bi₂O₃-TeO₂-P₂O₅ glasses depending on their composition.     

Surface tension of PbO-B2O3 and Bi2O3-B2O3 glass melts

The surface tensions of xPbO-(100?x) B₂O₃ (x = 30–80 mol%) and xBi₂O₃-(100?x) B₂O₃ (x = 0–100 mol%) melts were measured using the ring method over the temperature range 973 to 1373 K. The compositional and temperature dependences of surface tension were investigated. Addition of PbO and Bi₂O₃ to B₂O₃ increased the surface tensions of their respective PbO-B₂O₃ and Bi₂O₃-B₂O₃ melts. The surface tension showed a maximum at 60 mol% PbO in the PbO-B₂O₃ melts and at 70–80 mol% Bi₂O₃ in the Bi₂O₃-B₂O₃ melts. The temperature coefficient of surface tension was examined on the basis of its relationship to the structure, and it was suggested that the temperature coefficient of surface tension decreases with an increasing content of four-coordinated boron.     

Plasma spraying of Al2O3 and Al2O3Y2O3

A microstructural study has been carried out of plasma-sprayed Al₂O₃ and mixed and sintered Al₂O₃Y₂O₃. In order to ascertain the degree of metastability achieved by plasma spraying, these results are compared with a similar experiment utilizing a CO₂ laser for melting and the hammer-and-anvil technique for quenching of the same materials. X-ray diffraction methods were used to determine the obtained phases and crystal structures. In addition, transmission electron microscopy was used to confirm the phases present and to study their morpology. The porosity was studied with both mercury intrusion porosimetry and small angle neutron scattering. The addition of Y₂O₃ is shown to decrease the porosity from 15% to 7.5%. Adhesion is likewise related to the addition of Y₂O₃ and it is seen that adhesion of the mixture is measurably improved over that of pure Al₂O₃. The implication of these results is discussed.     

Electrical conduction through MIM structures of evaporated V2O5 and V2O5/B2O3 amorphous thin films

The electrical conduction through vacuum-evaporated thin films of V₂O₅ and V₂O₅/B₂O₃ in MIM structures has been investigated. The high-field behaviour of both types of film is in accordance with the Poole-Frenkel type of mechanism. The increase in B₂O₃ content in co-evaporated V₂O₅/B₂03 films results in a decrease in the conductivity of the composite films. This is attributed to the expansion of the resultant film structure due to the network-forming effect of B₂O₃. The covaporated thin films of V₂O₅/B₂O₃ with a molar content of B₂O₃ larger than 40% are observed to be unstable because of their hygroscopic nature.     

Electron spin resonance studies of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

Electron spin resonance studies of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ amorphous thin films have been made. For lower molar contents of B₂O₃, the co-evaporated V₂O₅/B₂O₃ films show poorly resolved hyperfine structure, whereas for higher content of B₂O₃ the hyperfine spectra are well resolved. This behaviour of films is attributed to the increase in the lifetime of a particular V⁴⁺ ion due to Anderson localization of charge, as the degree of disorder increases with increase in the molar content of B₂O₃. The unpaired electron at a given time is localized on a single ⁵¹V nucleus. The low intensity of ESR signal for higher concentration of V₂O₅ in the co-evaporated V₂O₅/B₂O₃ films has been related to the less effective concentration of V⁴⁺ ions due to antiferromagnetic coupling of the V⁴⁺ ions.     

The crystal structures and dielectric properties of Bi2O3 doped SrBi2Ta2O9 ceramics

Ferroelectric materials with Bi-layered structure such as SrBi₂Ta₂O₉ composition with excess x wt.% Bi₂O₃ (x = 0, 2, and 4) are investigated as the main composition, the effect of excess Bi₂O₃ content and sintering temperatures on the crystal structure and dielectric characteristics of SrBi₂Ta₂O₉ ceramics are developed. Even 1280 °C is used as the sintering temperature of stoichiometry SrBi₂Ta₂O₉ composition, the X-ray diffraction patterns will show that the SrBi₂Ta₂O₉ phase is coexisted with the raw material of Ta₂O₅ and the secondary phases of SrBi₂O₄ and BiTaO₄. For SrBi₂Ta₂O₉ composition with excess 2 wt.%- or 4 wt.%-Bi₂O₃-doped and sintered at 1040 °C, the Ta₂O₅, SrBi₂O₄, and BiTaO₄ phases are eliminated and only the SrBi₂Ta₂O₉ phase is observed in the X-ray diffraction patterns. It is found that sintering temperatures and excess Bi₂O₃ content have large influence on the grain growth, the bulk densities, the maximum dielectric constants, and the Curie temperatures of SrBi₂Ta₂O₉-based ceramics.     

Electrical conductivity of Cr2O3-doped Y2O3-stabilized ZrO2

The electrical conductivity of Cr₂O₃-doped Y₂O₃-stabilized ZrO₂ (YSZ) has been studied as functions of composition, temperature and oxygen pressure. The specimens have been prepared by hot preoning of co precipitated oxides to yield >99.7% density. The Cr₂O₃ added above the solubility limit ( 0.7 mol %) precipitated as a secondary phase at the grain boundaries. The conductivity of Cr₂O₃-doped YSZ was almost independent of the oxygen pressure in the range 10¹⁸ to 10⁵ Pa, indicating a dominant ionic condition. The electronic conductivity of dopant CR₂O₃ would be hindered by the higher ionic conductivity in thep _O2 ranges studied. The conductivity and the activation energy for conduction decreased slightly with the addition of Cr₂O₃. These phenomena seemed to be caused by vacancy trapping or polarization at the grain boundaries with the Cr₂O₃ precipitates. The samples with 1 mol % Cr₂O₃ addred to zirconia containing various Y₂O₃ contents showed similar conduction behaviour to those without Cr₂O₃ addition; that is, the conductivity maxima are observed at around 8 mol % Y₂O₃ addition to zirconia, and the activation energies increased with tha Y₂O₃ addition.     

Glass Formation in the BaO–La2O3–B2O3 System

The BaO · B₂O₃–La₂O₃ · B₂O₃ and 3BaO · B₂O₃–La₂O₃ · 3B₂O₃ joins of the ternary system BaO–La₂O₃–B₂O₃ are studied using x-ray diffraction and density measurements. The boundary of the glass-forming region is shown to pass near ternary eutectic compositions. The existence of the compound 3BaO · La₂O₃ · 2B₂O₃ is confirmed.     

Compositional dependence of infrared absorption spectra studies for TeO2-P2O5 and TeO2-P2O5-Bi2O3 glasses

The infrared absorption spectra of the vitreous TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ systems are studied in the spectral region of 4000 to 200 cm^–1. Absorption bands in this range are assigned. The midband wavenumber and the absorption intensity for the attributed bands are found to be strongly and systematically dependent on glass composition. Quantitative analysis was also attempted to justify our attribution of the observed bands.     

Subsolidus,high temperature phase relations in the systems Al2O3-Cr2O3-ZrO2, MgO-Cr2O3-ZrO2 and MgO-Al2O3-ZrO2

In the temperature range 1600 to 1900° C, the system A₂O₃-Cr₂O₃-ZrO₂ is characterized by the coexistence of ZrO₂ (unstablilized) and an (Al, Cr)₂O₃ solid solution series. In the systems MgO-Cr₂O₃-ZrO₂ and MgO-Al₂O₃-ZrO₂ a nearly stoichiometric spinel coexists with both stabilized and unstabilized ZrO₂. At temperatures above 1600°C a new ternary Mg-Al-Zr oxide becomes stable in the MgO-rich part of the MgO-Al₂O₃-ZrO₂ system.     

Microstructure and mechanical properties of Al2O3-Cr2O3-ZrO2 composites

Al₂O₃ is a popular ceramic and has been used widely in many applications and studied in many aspects. On the other hand, zirconia-toughened alumina (ZTA) is a desirable material for engineering ceramics because of its high hardness, high wear resistance and high toughness. In the present research, Al₂O₃-Cr₂O₃-ZrO₂ composites were produced by hot-pressing in order to harden the Al₂O₃ matrix in ZTA. Its microstructure and mechanical properties were studied by SEM, ESCA, XRD, Vickers hardness and bending strength test. It was found that addition of ZrO₂ inhibited the grain growth of Al₂O₃-Cr₂O₃ and the grain growth of ZrO₂ proceeded with increasing amounts of ZrO₂ in the Al₂O₃-Cr₂O₃-Zr₂ composite. The formation of solid solution Al₂O₃-Cr₂O₃ was also confirmed by XRD, and monoclinic ZrO₂ increased on addition of Cr₂O₃. Maximum hardness was at Al₂O₃-10wt% Cr₂O₃ with 10 vol% ZrO₂ and a stress-induced transformation was confirmed on the fracture surface of the specimen after the bending test.     

Depolymerization of GeO2 and GeO2 · Sb2O3 glasses by Bi2O3

Glasses that contain at least 60 mol% GeO₂ were prepared in the Bi₂O₃ · GeO₂ and Bi₂O₃ · Sb₂O₃ · GeO₂ systems. Their densities, refractive indices, and infra-red spectra were recorded. Negative molar volume deviations and positive refraction deviations occur for all of the binary glasses. These create deviations for the 60 to 80 mol % GeO₂ ternary glasses that indicate non-ideal mixing when Sb³⁺ substitutes for Bi³⁺. Also, the main Ge-O stretching vibration shifts to as low as 695 cm^?1 for the Bi₂O₃-rich binary and ternary glasses. All of these findings show that Bi₂O₃ more effectively depolymerizes GeO₂ than does Sb₂O₃. The probable structural reasons for this behaviour are discussed.     

DSC study on the phase transition of BaSm2Mn2O7 and BaEu2Mn2O7

The phase transition of BaSm₂Mn₂0₇ and BaEu₂Mn₂O₇ were studied by differential scanning calorimetry (DSC). Transition temperatures and enthalpy changes accompanying the phase transition for stoichiometric BaSm₂Mn₂O₇ and BaEu₂Mn₂0₇ were measured. The transition temperatures, 525K and 550K for BaSm₂Mn₂O₇ and BaEu₂Mn₂O₇, respectively, determined in this study, are in good agreement with the previous results of high temperature X-ray diffractometry. The enthalpy changes of the transition between orthorhombic and tetragonal structures, ΔH_tr^O, were 0.6 kJ/mol and 1.9 kJ/mol for BaSm₂Mn₂O₇ and BaEu₂Mn₂O₇, respectively.     

New low loss microwave dielectric ceramics in the BaO-TiO2-Nb2O5Ta2O5 system

Microwave ceramic dielectric resonator materials in the BaO-TiO₂-Nb₂O₅Ta₂O₅ system such as BaTiNb₄O₁₃, BaTiTa₂Nb₂O₁₃, BaTiTa₄O₁₃, Ba₃Ti₄Nb₄O₂₁, Ba₃Ti₄Ta₄O₂₁, Ba₃Ti₅Nb₆O₂₈, Ba₃Ti₅Ta₆O₂₈ and Ba₃Ti₅Nb₃Ta₃O₂₈ have been prepared by the conventional solid state ceramic route. They have relatively high dielectric constant and high quality factor. The resonator materials are characterized by X-ray diffraction and scanning electron microscopy (SEM) methods. The BaTiNb₄O₁₃Ba₃Ti₅Nb₆O₂₈ and Ba₃Ti₅Nb₃Ta₃O₂₈ have small temperature variation of the resonant frequency and are possible microwave dielectric resonator materials for practical applications.     

An infrared study of the Na2O-V2O5-Fe2O3 glass system

Structural studies of Na₂O-V₂O₅-Fe₂O₃ glasses have been made from their IR spectra which show that vibrational bands characteristic of the vanadium-oxygen bonds in V₂O₅ are maintained in these glasses, but the addition of Na₂O to these glasses results in a shifting of the higher frequency peaks towards lower wave number due to structural changes produced in V₂O₅. It is inferred that Na⁺ ions make bonds interstitially with isolated V=O bonds and VO₅ polyhedra are destroyed, resulting in the formation of VO₄ polyhedra through intermediate complexes. The variation of Fe₂O₃, however, produces an insignificant structural change in these glasses. The IR spectra of samples heated to their temperature of crystallization confirm the formation of a series of complexes with several isolated V=O bonds.     

Infrared absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The Fourier transform infrared spectra of different compositions of evaporated V₂O₅/B₂O₃ thin films have been investigated. Most of the absorption bands corresponding to V₂O₅ and B₂O₃ films coincide with those reported by other authors. The short-range order in amorphous V₂O₅ films is found to be conserved. The absorption spectra indicate a boroxol ring structure for B₂O₃ films. In co-evaporated V₂O₅/B₂O₃ films the boron is observed to substitute in the V₂O₅ network such that the coordination number of vanadium ion remains unchanged. The presence of a number of bands corresponding to -OH groups indicates the hygroscopic character of the films.     

A.c. conduction through MIM sandwich samples of evaporated thin films of V2O5 and V2O5/B2O3

The a.c. electrical properties of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ films have been investigated. The conductivity in both types of film follows the theory of Elliott for single polaron hopping. The behaviour of capacitance, tangent of loss angle and dielectric loss agrees with the model proposed by Goswami and Goswami. The co-evaporated films of V₂O₅/B₂O₃ show better dielectric properties than simple V₂O₅ with increasing content of B₂O₃. Because of their hygroscopic character, the films with B₂O₃ content larger than 40% are observed to be unstable in the atmosphere.     

Synthesis of the clinopyroxenes join CaMgSi2O6-NaAlSi2O6 for jewellery

Clinopyroxenes of the join CaMgSi₂O₆(diopside)-NaAlSi₂O₆ (jadeite) were synthesized in the temperature range 800–1900C and under varying pressure, 10–55 kbar. The stability regions of various compositions of diopside-jadeite have been established experimentally using different compositions of glass materials: stoichiometric composition NaAlSi₂O₆, 0.1CaMgSi₂O₆-0.9NaAlSi₂O₆, 0.2CaMgSi₂O₆-0.8NaAlSi₂O₆, 0.3CaMgSi₂O₆-0.7NaAlSi₂O₆, and 0.4CaMgSi₂O₆-0.6NaAlSi₂O₆. Unit cell parameters of synthetic clinopyroxenes with the above compositions were determined. The physical properties, such as hardness, toughness, density, and refractive index, etc., were also measured. The results show that synthetic clinopyroxenes have the same properties as the natural one. The gem quality of diopside-jadeite clinopyroxenes was achieved by synthesised on the basis of the above experiments. Various colouring agents, such as Cr₂O₃, Co₂O₃, NiO₂, Fe₂O₃, TiO₂, MnO, CuO, and their combinations, FeO-Cr₂O₃, etc., were added to obtain the different colours of gem. In addition, small amounts of the rare-earth oxides, such as CeO₂, Nd₂O₃, Sm₂O₃, Dy₂O₃, Eu₂O₃, Er₂O₃, Pr₆O₁₁, Lu₂O₃ and CuO-Eu₂O₃, Co₂O₃-Nd₂O₃, etc., were also added to produce fluorescent clinopyroxenes for jewellery.