Phase relations in the SrO–Ga2O3–B2O3 system

The subsolidus phase relations in the SrO–Ga₂O₃–B₂O₃ system were investigated. The system contains 10 binary compounds and two ternary compounds, and can be divided into 15 three-phase regions. The new ternary compound SrGaBO₄ has two modifications (- and β-phases), both of which crystallize in the orthorhombic system but with different space groups.     

Thermochemistry of GaBO3 and phase equilibria in the Ga2O3–B2O3 system

Employing a Tian-Calvet-type calorimeter operating in the scanning mode at temperatures from 1120 to 1220 K, the enthalpy change, Δ_dH, associated with the decomposition of GaBO₃ (=1/2β-Ga₂O₃+1/2B₂O₃(liq.)) and the corresponding decomposition temperature, T_d, were determined: Δ_dH=30.34±0.6 kJ/mol, T_d=1190±5 K. Using the transposed-temperature-drop method the thermal enthalpy, H(T)−H(295 K), of GaBO₃ was measured as a function of temperature, T, in the region from 760 to 1610 K; the results obtained are

[H(T)−H(295 K)]/(J/mol)=104.8·(T/K)−31 300 (760 K<T<1190 K),

[H(T)−H(295 K)]/(J/mol)=138.8·(T/K)−41 480 (1190 K<T<1590 K).

On the basis of the experimental results, the enthalpy and entropy of formation, Δ_fH and Δ_fS, respectively, of GaBO₃ from the component oxides were derived:

Δ_fH=−30.34 kJ/mol,Δ_fS=−25.50 J/(K·mol) at 1190 K,

Δ_fH=−10.55 kJ/mol,Δ_fS=−5.48 J/(K·mol) at 298 K.

The enthalpy versus temperature curve shows, apart from a step associated with the decomposition of GaBO₃, a further step at 1593 K which is attributed to a monotectic equilibrium.     

Subsolidus phase relations in the ZnO–MoO3–B2O3, ZnO–MoO3–WO3 and ZnO–WO3–B2O3 ternary systems

The subsolidus phase relations in the ZnO–MoO₃–B₂O₃, ZnO–MoO₃–WO₃ and ZnO–WO₃–B₂O₃ ternary systems have been investigated by the means of X-ray powder diffraction (XRD). There is no ternary compound in all the systems. There are five binary compounds and five tie lines in the ZnO–MoO₃–B₂O₃ system. This system can be divided into six 3-phase regions. There are three binary compounds and three tie lines in the ZnO–MoO₃–WO₃ system. This system can be divided into four 3-phase regions. There are four binary compounds and four tie lines in the ZnO–WO₃–B₂O₃ system. This system can be divided into five 3-phase regions. The possible component regions for ZnO single crystal flux growth were discussed. The phase diagram of Zn₃B₂O₆–ZnWO₄ pseudo-binary system has been constructed, and the result reveals this system is eutectic system. The eutectic temperature is 1007 °C and eutectic point component is 70 mol% Zn₃B₂O₆.     

Thermodynamic study of CVD–ZrO2 phase diagrams

Chemical vapor deposition (CVD) of zirconium oxide (ZrO₂) from zirconium acetylacetonate Zr(acac)₄ has been thermodynamically investigated using the Gibbs’ free energy minimization method and the FACTSAGE program. Thermodynamic data Cp°, ΔH° and S° for Zr(acac)₄ have been estimated using the Meghreblian–Crawford–Parr and Benson methods because they are not available in the literature. The effect of deposition parameters, such as temperature and pressure, on the extension of the region where pure ZrO₂ can be deposited was analyzed. The results are presented as calculated CVD stability diagrams. The phase diagrams showed two zones, one of them corresponds to pure monoclinic phase of ZrO₂ and the other one corresponds to a mix of monoclinic phase of ZrO₂ and graphite carbon.     

Phase diagram of the CuGaSe2–SiSe2 and CuInSe2–SiSe2 systems

The phase diagrams of the CuGaSe₂–SiSe₂ and CuInSe₂–SiSe₂ systems were constructed using the results of differential thermal and X-ray phase analysis. Both systems are of the eutectic type with the eutectic point coordinates 75 mol% SiSe₂, 1042 K (CuGaSe₂–SiSe₂); 67 mol% SiSe₂, 1083 K (CuInSe₂–SiSe₂). Solid solutions based on CuGaSe₂ and CuInSe₂ were discovered in these systems; their extent at 670 K being 24 and 25 mol% SiSe₂, respectively. The crystal structure of the limiting compositions of these solid solutions was refined.     

Thermodynamic modeling of the CeO2–CoO phase diagram

A thermodynamic modeling of the CeO₂–CoO phase diagram was performed with recent experimental data. The excess Gibbs energies of the solution phases were described on the basis of the simple regular solution. A consistent set of optimized interaction parameters was derived for describing the Gibbs energy of each phase in this system leading to a good fit between calculation and experimental data. The liquidus, solidus, and solvus curves were calculated and also the lattice stabilities of the components were evaluated.     

Formation of celsian from mechanically activated BaCO3–Al2O3–SiO2 mixtures

A ternary mixture BaCO₃–Al₂O₃–SiO₂ was mechanically activated for different lengths of time. Chemical composition of the mixture corresponded to BaAl₂Si₂O₈–BAS. As a function of activation time, reaction course was followed in the temperature range 750–1200°C. Reaction of celsian formation was followed using thermogravimetry as well as conventional and high-temperature X-ray diffractometry. The obtained data show that reaction rate increases with prolonged activation time, under the same conditions of thermal treatment. Formation of hexacelsian via a series of solid state reactions involving Ba-silicates, was favoured with increasing activation time. Direct formation of monoclinic celsian was retarded, however, with prolonged activation.     

Phase diagram of In2Te3–Cr3Te4

Based on the results of a physico-chemical analysis, the equilibrium diagram of the In₂Te₃–Cr₃Te₄ section of the In–Cr–Te ternary system has been constructed. The section is quasi-binary and at the basic component ratio of 1:1 the ternary compound In₂Cr₃Te₇ with a peritectic melting character is formed. Both basic components at 300 K have homogeneity regions with limits of 5.5 and 2 mol% from the In₂Te₃ and Cr₃Te₄ sides, respectively.     

The ternary system: H2O–Fe(NO3)3–Co(NO3)2 isotherms −15 and −25 °C

The binary system H₂O–Fe(NO₃)₃ has been investigated at temperature ranging between –25 and 47 °C.The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied at −15 and −25 °C by using a synthetic method based on conductivity measurements which allows all the characteristic points of the isotherms to be determined, and the stable solid phases which appear are respectively: ice, Fe(NO₃)₃·9H₂O, Fe(NO₃)₃·6H₂O, Co(NO₃)₂·9H₂O, Co(NO₃)₂·6H₂O and Co(NO₃)₂·3H₂O.     

Dielectric dispersion in Li2O–MoO3–B2O3 glass system doped with V2O5

Li₂O–MoO₃–B₂O₃ glasses containing different amounts of V₂O₅, ranging from 0 to 1.5 mol%, were prepared. The dielectric properties (viz., constant ′, loss tan δ, AC conductivity σ_ac over a wide range of frequency and temperature) have been studied as a function of the concentration of vanadium ions. The variation of AC conductivity with the concentration of V₂O₅ passes through a maximum at 0.8 mol% V₂O₅. In the high-temperature region, the AC conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The dielectric relaxation effects exhibited by these glasses have been analyzed quantitatively by pseudo Cole–Cole plot method and the spreading of relaxation times has been established. Further analysis of these results has been carried out with the aid of the data on ESR, IR and optical absorption spectra.     

Low temperature sintering and properties of CaO–B2O3–SiO2 system glass ceramics for LTCC applications

The P₂O₅ + ZnO, ZrO₂ + TiO₂, B₂O₃ and a low-melting-point CaO–B₂O₃–SiO₂ glass (LG) are selected as the sintering additives, and the effect of their additions on the microwave dielectric properties, mechanical properties and microstructures of CaO–B₂O₃–SiO₂ system glass ceramics is investigated. It is found that the sintering temperature of pure CBS glass is higher than 950 °C and the sintering range is about 10 °C. With the above additions, the glass ceramics can be sintered between 820 °C and 900 °C. The dielectric properties of the samples are dependent on the additions, densification and microstructures of sintered bodies. The major phases of this material are CaSiO₃, CaB₂O₄ and SiO₂. With 10 wt% B₂O₃ and LG glass additions, the CBS glass ceramics have better mechanical properties, but worse dielectric properties. The _r values of 6.51 and 7.07, the tan δ values of 0.0029 and 0.0019 at 10 GHz, are obtained for the CBS glass ceramics sintered at 860 °C with 2 wt% P₂O₅ + 2 wt% ZnO and 2 wt% ZrO₂ + 2 wt% TiO₂ additions, respectively. This material is suitable to be used as the LTCC material for the application in wireless communications.     

Optical study of a new phase LaGa3O6:RE (RE=Pr, Nd, Eu) in the La2O3–Ga2O3 system

The absorption and emission spectroscopies of RE³⁺ ions embedded in a new phase, LaGa₃O₆, owing to the La₂O₃–Ga₂O₃ binary system (RE=Pr, Nd, Eu) are discussed. The ^2S+1L_J level degeneracies are completely lifted in accordance with the low point symmetry of the site occupied by the rare earth ion in LaGa₃O₆. The energy level schemes deduced from the data are reproduced by considering a crystal field (CF) effective Hamiltonian involving the nine real and five imaginary parameters required for the C₂ or C_s symmetry of the rare earth site. The rms deviation is satisfactory for the three simulations. However, the strong variation of the CF parameters between Pr³⁺ and Eu³⁺ in LaGa₃O₆ suggests the possible limit of existence of the phase, intimately correlated to small variations of the rare earth ionic radius.     

Er-doped SiO2–Al2O3 thin films prepared by the sol–gel route

The synthesis of homogeneous and pure silica–alumina binary glasses doped with rare-earth (RE) ions such as Er³⁺ is currently a key challenge for the development of integrated optics devices such as lasers, optical amplifiers or waveguides. In this study Er³⁺-doped SiO₂–Al₂O₃ films were prepared by the sol–gel route. Aluminium sec-butoxide, Al(O-sec-C₄H₉)₃ (ASB), and tetraethoxysilane, Si(OC₂H₅)₄ (TEOS), were used as glass oxide precursors, whereas erbium was introduced as Er(NO₃)₃. The alumina content in the silica matrix was 10 at.%, while erbium doping ranged between 200 and 5000 ppm. The preparation of the starting sol–gel solution and the layer deposition by a dip-coating procedure were performed in dry-box under nitrogen atmosphere. The obtained films were subsequently annealed in air between 300 and 1000 °C. After treatment at 500 °C, layers 200 nm thick were obtained. The composition, microstructure and surface morphology of the films were investigated by X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), glancing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). Crack-free, transparent, high purity films were obtained, characterised by compositional and microstructural homogeneity.     

Processing and properties of ZrO2(3Y2O3)–Al2O3 nanocomposites

Nanocomposites of yttria-stabilized zirconia (YSZ), containing 20 and 40 wt% alumina, were prepared by a two-step process: (1) fine-particle aggregates of the constituent phases were melted and homogenized in a high enthalpy plasma, prior to rapid quenching in water to obtain metastable starting powders, and (2) the metastable powders were consolidated by hot isostatic pressing (HIP), under conditions designed to ensure the formation of nanocomposites by controlling the metastable-to-stable phase transformation during sintering. In both cases, the resulting nanocomposites had completely uniform structures, comprising 27 and 50 vol% of -Al₂O₃ in a tetragonal YSZ matrix phase. Measurements of hardness and indentation toughness were correlated with observed structures.     

The reduction of Eu to Eu in air and luminescence properties of Eu activated ZnO–B2O3–P2O5 glasses

A valence change from Eu³⁺ to Eu²⁺ was observed in the europium ion-doped ZnO–B₂O₃–P₂O₅ glasses prepared at high temperature in air. The fluorescence emission spectrum of the sample consists of a broad emission band ascribed to the 5d–4f transition of Eu²⁺ ion and sharp emission peaks assigned to the transitions of ⁵D_o–⁷F_J (J = 0, 1, 2, 3, and 4) of Eu³⁺ ion, indicating that part of Eu³⁺ can be reduced into Eu²⁺ in the glass. A charge compensation model is proposed. The rigid tetrahedral network structure of glasses plays an important role in stability of Eu²⁺. The fabrication conditions are also studied.     

Role of titanium valence states in optical and electronic features of PbO–Sb2O3–B2O3:TiO2 glass alloys

PbO–Sb₂O₃–B₂O₃ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 1.5 mol.%) were synthesized. The samples are characterized by X-ray diffraction, scanning electron microscopy and DSC techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra, magnetic susceptibility, photo-induced birefringence (PIB) and dielectric properties (constant ′, loss tan δ, a.c. conductivity σ_ac over a wide range of frequency and temperature) of these glass–ceramics have been explored. The analysis of these results indicated that Ti ion surrounding ligands play principal role in the observed PIB and the sample crystallized with 0.8 mol.% of TiO₂ is the most suitable for the applications in non-linear optical devices.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10⁻³ atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Thermodynamics and phase diagrams in the binary systems Na2O-SiO2, Na2O-GeO2, Na2O-B2O3, Li2O-B2O3, CaO-B2O3, SrO-B2O3, and BaO-B2O3

We applied our model to the enthalpy of mixing data of the binary systems Na₂O-SiO₂, Na₂O-GeO₂, Na₂O-B₂O₃, Li₂O-B₂O₃, CaO-B₂O₃, SrO-B₂O₃, and BaO-B₂O₃. The most stable composition in the liquid, that is where the enthalpy of mixing is most negative, is with a metal-oxygen ratio of 4 to 3, for monovalent metals (Na and Li) and 3 to 4 for divalent metals (Ba and Ca) in liquid silicates or borates. The same applies to the CaO-SiO₂, CaO-Al₂O₃, PbO-B₂O₃, PbO-SiO₂, ZnO-B₂O₃, and ZnO-SiO₂ systems. The oxygen to metal ratio, its constant value in various types of systems, reflects and describes the structure of the liquid. Using the analyzed enthalpies of mixing data and the available phase diagrams, we calculated the enthalpies of formation of the various binary compounds. The results are in excellent agreement with data in the literature that were obtained from direct solid-solid calorimetry.     

Subsolidus phase relations in the system ZnO–P2O5–MoO3

The subsolidus phase relations of the ternary system ZnO–P₂O₅–MoO₃ were investigated by means of X-ray diffraction (XRD). Seven binary compounds and eight 3-phase regions were determined, and no ternary compound was found in this system. The phase diagram of pseudo-binary system Zn₃(PO₄)₂–Zn₃Mo₂O₉ was also constructed through XRD and differential thermal analysis (DTA) methods, and the result reveals this system is eutectic system. The eutectic temperature is 904 °C and the corresponding component is 30% Zn₃Mo₂O₉ and 70% Zn₃(PO₄)₂.     

Properties of ZrO2–Al2O3 composite as a function of isothermal holding time

Zirconia and alumina based ceramics present interesting properties for their application as implants, such as biocompatibility, good fracture resistance, as well as high fracture toughness and hardness. In this work the influence of sintering time on the properties of a ZrO₂–Al₂O₃ composite material, containing 20 wt% of Al₂O₃, has been investigated. The ceramic composites were obtained by sintering, in air, at 1600 °C for sintering times between 0 and 1440 min. Sintered samples were characterized by microstructure and crystalline phases, as well as by mechanical properties. The grain growth exponents, n, for the ZrO₂ and Al₂O₃ were 2.8 and 4.1, respectively, indicating that different mechanisms are responsible for grain growth of each phase. After sintering at 1600 °C, the material exhibited a dependency of hardness as function of sintering time, with hardness values between 1500 HV (120 min) and 1310 HV (1440 min) and a fracture toughness of 8 MPa m^1/2, which makes it suitable for bioapplications, such as dental implants.