Ionic conduction in solid solution of the system La2O3-CaF2

The crystal phase and the electrical conduction in sesquioxide-alkaline earth difluoride systems were investigated. LaOF-type cubic solid solution was found in the system La₂O₃-CaF₂. This phase showed anion conductivity comparable to that of YF₃-doped CaF₂. Electrolysis by Tubandt's method showed that the conduction was predominantly attributed to fluoride ions. In this solid electrolyte, the fluoride ion is easily substituted by oxide ion through cathode reaction in the oxygen atmosphere.     

Oxide ion and electron mixed conduction in the fluorite-type cubic solid solution in the system Bi2O3-Tb2O3.5

Electrical conduction in sintered oxides of the system Bi₂O₃-Tb₂O_3.5 has been investigated. Oxide ion conduction was observed in the rhombohedral (low temperature) phase and the f c c (high temperature) phase present in the composition range less than 20mol% Tb₂O_3.5. The fcc phase could be stabilized at lower temperatures by adding more than 30 mol % Tb₂O_3.5. In addition to oxide ion conduction, appreciable electronic conduction appeared in this composition range. The oxide ion transport number of this phase decreased with increasing content of Tb₂O_3.5 and the specimens having 40–50 mol % Tb₂O_3.5 showed mixed conduction where electrical conduction was comparably contributed by oxide ions and electrons. Electronic conduction in the fee phase was considered to be due to the change in valence of terbium at high temperatures.     

High oxide ion conduction in sintered Bi2O3 containing SrO,CaO or La2O3

Ionic conduction in sintered oxides of the system Bi₂O₃-SrO was investigated by measuring the conductivity and ion transference number under various conditions. The ion transference numbers were measured by an oxygen concentration cell employing the specimen as the electrolyte.It was found that the solid solution containing 2040 mole% SrO which had a rhombohedral structure was an almost pure oxide ion conductor under a relatively high partial pressure of oxygen, and that the conductivity was several times higher than that of stabilized zirconias at the same temperatures up to 800°C. Oxide ion conduction was confirmed also by quantitative determination of generated O₂ from the anode of the oxygen concentration cell during discharge.The sintered specimens of the systems Bi₂O₃-CaO and Bi₂O₃-La₂O₃ were found also to be oxide ion conductors, and the ion transference numbers were greater than 0.9.     

High oxide ion conduction in sintered oxides of the system Bi2O3-Y2O3

The ionic conduction in sintered Bi₂O₂-Y₂O₃ was investigated by measuring the conductivity and the emf of an oxygen concentration cell using the specimen tablet as electrolyte. The face centred cubic phase in this system was found to show high oxide ion conduction accompanied by a little electronic conduction when exposed to air. This phase was stable with a composition of 25 ～ 43 mol % Y₂O₃ over a wide range of temperatures, and the oxide ion conductivity increased with decrease in Y₂O₃. The conductivities of (Bi₂O₃)_0.75 (Y₂O₃)_0.25 were 1.6×10^?1 Ω^?1 cm^?1 at 700°C and 1.2×10^?2 Ω^?1 cm^?1 at 500°C values which are many times higher than those of stabilized zirconia (ZrO₂)_0.90(Y₂O₃)_0.10 at corresponding temperatures. Specimens containing less than 25 mol % Y₂O₃ showed a phase transition at 700 ～ 580°C and the conductivities decreased remarkably below these temperatures. High oxide ion conduction in the fcc phase is attributed to the migration of oxide ion vacancies which were present in an appreciable amount.     

High oxygen ion conduction in sintered oxides of the Bi2O3-Er2O3 system

The phase diagram of the Bi₂O₃-Er₂O₃ system was investigated. A monophasic f c c structure was stabilized for samples containing 17.5–45.5 mol% Er₂O₃. Above and below this concentration range polyphasic regions appear. The f c c phase showed high oxygen ion conduction. The ionic transference number is equal to one for specimens containing 30 mol% Er₂O₃ or less, while an electronic component is introduced at low temperatures for specimens containing 40–60 mol% Er₂O₃. Between 673 K and 873 K a maximum in the conductivity was found at 20 mol% Er₂O₃. (Bi₂O₃)_0.8.(Er₂O₃)_0.20 is found to be the best oxygen ion conductor so far known. The conductivity at 773 K and 973 K is 2.3 ^–1m^–1 and 37 ^–1 m^–1 respectively. These values are 2–3 times higher than the best oxygen ion conductor reported for substituted Bi₂O₃ systems and 50–100 times higher than those of stabilized zirconia (ZrO₂)_0.915(Y₂O₃)_0.085 at corresponding temperatures.     

High oxide ion conduction in the sintered oxides of the system Bi2O3-Gd2O3

In order to characterize the conduction behaviour in the sintered oxides of the system Bi₂O₂-Gd₂O₃, the electrical conductivity in air and the emf of the oxygen concentration cell were measured. The new rhombohedral phase found in this system exhibited high oxide ion conduction especially at relatively high oxygen pressure. The rhombohedral phase was stable in the composition range between 10 and 30 mol% Gd₂O₃ below 600° C and was transformed into the face-centred cubic phase with rising temperature, the conduction in which was by oxide ion as in the rhombohedral phase. At concentrations greater than 35 mol% Gd₂O₃, the fcc phase was stable over a wide range of temperature (～900° C) and kept its high oxide ion conduction. The conductivities of rhombohedral (Bi₂O₃)_0.90(Gd₂O₃)_0.10 and fcc (Bi₂O₃)_0.65(Gd₂O₃) _0.35 ^* are 4.5 and 2.4×10^?2 cm^?1 at 600°C, respectively. These are about one order of magnitude higher than that of the well-known yttria-stabilized zirconia at corresponding temperatures. High-oxide ion-conduction in the rhombohedral and fcc phase was considered to be due to the appreciable numbers of oxide ion vacancies in these crystals.     

Phase diagram study and thermodynamic modeling of the MgO-Y2O3-MgF2-YF3 system

The phase diagram of the MgO-Y₂O₃-MgF₂-YF₃ system (Mg,Y//O,F reciprocal system) at 1273–1773 K was investigated for the very first time using a classical equilibrium/quenching and differential thermal analysis (DTA) experiments followed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analyses. No ternary or quaternary crystalline phase was found, and the eutectic reactions in the reciprocal system were identified. The overall phase diagram of the reciprocal system was also calculated based on the thermodynamic modeling using the CALculation of PHAse Diagram (CALPHAD) method.     

Energetics and structure of the B-type solid solution in the Nd2O3–Y2O3 system

The system Nd₂O₃–Y₂O₃ contains solid-solution phases with several different structures. Single-phase B-type (Nd_1−xY_x)₂O₃ solid solutions in the range of $0.2\le x\le 0.5$ were formed at 1873 K and retained on cooling to ambient temperature. They showed a linear composition dependence of lattice parameters, enabling extrapolation to x = 0 and 1 for comparison with the structures of the stable endmembers. A positive enthalpy of formation from A-type Nd₂O₃ and C-type Y₂O₃ determined using oxide melt solution calorimetry indicated entropic stabilization of the B-type phase. A positive interaction parameter for mixing in the B-type solid solution, Ω $=$ 47.46 ± 4.04 kJ/mol, was obtained by fitting the data using a regular solution model. This value is significantly more positive than that obtained by previous phase diagram analysis using the CalPhaD approach. Exsolution into two B-type phases is predicted to occur below 1427 K, making it unimportant for the equilibrium phase relations that will be dominated by other structures at low temperature.     

High oxide ion conduction in sintered oxides of the system Bi2O3-WO3

The ionic conduction in sintered oxides of the system Bi₂O₃-WO₃ was investigated by measuring conductivities and ion transference numbers under various conditions. The ion transference number was measured by an oxygen concentration cell employing the specimen tablet as the electrolyte.It was found that a compound 3Bi₂O₃ WO₃ and its solid solution were high oxide ion conductors, the conductivities of which were about one order of magnitude higher than those of the well-known oxide ion conductors such as stabilized zirconias. In contrast to pure Bi₂O₃ which is a completely electronic conductor below 730°C, these materials showed high oxide ion conduction even below 700°C accompanied by little electronic conduction. 3Bi₂O₃ WO₃ has the face centered cubic structure, probably of the fluorite type, and the oxide ion conduction was thought to be attributed to the migration of oxide ion vacancies in the crystal.     

Nanocrystaline solid solution CeO2–Bi2O3

Nanocrystalline powders of solid solution CeO₂–Bi₂O₃ were synthesized by self-propagating room temperature reaction (SPRT) procedure with composition (Ce_1?xBi_xO_2?δ where the x = 0.1–0.5). X-ray diffraction analyses show that for x < 0.50 a solid solution with fluorite structure is formed. Rietveld's structure refinement method was applied to characterize prepared powders and its microstructure (size–strain). The lattice parameters increase according to Vegard's rule with increasing of Bi concentration. The average crystallite size is about 2–3 nm. Spectroscopic ellipsometry and Raman scattering measurements were used to characterize the samples at room temperature. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas increase of Bi content provokes a small decrease of optical absorption edge in comparison with pure ceria. Specific surface area of obtained powders was measured by Brunauer–Emmet–Teller (BET) method.     

Effects of B2O3 on microstructure and ionic conductivity of Li6.5La3Zr1.5Nb0.5O12 solid electrolyte

Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZN) garnet-type structure was synthesized at low temperature with B₂O₃ addition by solid state reaction method. The effects of B₂O₃ content on the formation, microstructure, ionic conductivity and activation energy of the LLZN solid electrolytes have been investigated by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and alternate current (AC) impedance spectroscopy. The cubic LLZN phase was obtained after calcining at 850 °C for 6 h and no phase evolution was observed after sintering at 1100 °C for 6 h. The relative density and lithium ion conductivity increased first and then decreased with increasing B₂O₃ content, reaching the maximum value of 92.4% and 1.86×10⁻⁴ S cm⁻¹ respectively in the sample with 1.4 wt% B₂O₃. By contrast, the activation energy reached a minimum value of ~31.5 kJ mol⁻¹.     

Synthesis and characterization of a pyrochlore solid solution in the Na2O-Bi2O3-TiO2 system

The compositional limits of a previously reported (J. Am. Ceram. Soc., 61, 5-8. (1978)) but relatively unstudied sodium-bismuth titanate pyrochlore solid solution are revised and their electrical properties presented. The pyrochlore solid solution we report forms via a different mechanism to that originally reported and occurs in a different location within the Na₂O-Bi₂O₃-TiO₂ ternary system. In both cases, relatively large amounts of vacancies are required on the A-sites and on the oxygen sites, similar to that reported for undoped ‘Bi₂Ti₂O₇’ pyrochlore. In contrast to ‘Bi₂Ti₂O₇’, this ternary pyrochlore solid solution can be prepared and ceramics sintered using conventional solid-state methods; however, the processing requires several challenges to be overcome to obtain dense ceramics. This cubic pyrochlore series has low electrical conductivity (and does not exhibit any evidence of oxide-ion conduction) and exhibits relaxor ferroelectric behavior with a broad permittivity maximum of ~100 near room temperature. Variable temperature neutron diffraction data do not provide any conclusive evidence for a phase transition in the pyrochlore solid solution between ~4 and 873 K.     

Phase diagram of the Al2O3–ZrO2–La2O3 system

The phase diagram of the Al₂O₃–ZrO₂–La₂O₃ system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Three new ternary and two new binary eutectics were found. The minimum melting temperature is 1665 °C and it corresponds to the ternary eutectic LaAlO₃ + T-ZrO₂ +  La₂O₃·11Al₂O₃. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al₂O₃–ZrO₂–La₂O₃ system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. The latter fact is the theoretical basis for creating new composite ceramics with favorable properties in the Al₂O₃–ZrO₂–La₂O₃ system.     

Structural-chemical mechanism of formation of solid solutions in the La2SrAl2O2-Ho2SrAl2O7 system

The processes of phase formation in the La₂O₃-Ho₂O₃-SrO-Al₂O₃ system are investigated in the temperature range 1200–1500°C. The structural characteristics of the compounds described in the studied system are presented. It is established that the formation of (La_1?x Ho_x)₂SrAl₂O₇ solid solutions proceeds through the formation of LaAlO₃, LaSrAlO₄, SrAl₂O₄, and SrHo₂O₄ compounds. An increase in the holmium content and the temperature leads to a crossover from the mechanism in which the interaction of LaAlO₃ and LaSrAlO₄ is a limiting stage to the mechanism in which the decisive role is played by the interactions of SrAl₂O₄ with Ho₂O₃ and SrHo₂O₄ with Al₂O₃.     

Fabrication of nanocrystalline Sc2O3-Y2O3 solid solution ceramics by spark plasma sintering

Sc₂O₃-Y₂O₃ solid solution (SYSS) ceramics with novel nanocrystalline structures have been successfully fabricated by spark plasma sintering (SPS) method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR and indentation techniques. The SYSS ceramics can possess high hardness by keeping their excellent infrared transmission performance. Especially, the transmittance of as-obtained SYSS ceramics can exceed as high as 80% in the infrared region of 2–6 µm. Moreover, the Vickers hardness is increased to 9.18 GPa by increasing the addition ratio of Sc₂O₃ to 20 at%. Here, it is very important to point out that the mechanical strength of yttria ceramics can be evidently enhanced without deteriorating their optical transmission performance by the addition of Sc₂O₃ as well as the application of SPS technique, where the solid solution strengthening and fine grain strengthening are involved during the synthesis process, respectively.     

Phase equilibria in the La2O3-Sm2O3-ZrO2 system: Experimental studies and thermodynamic modeling

A series of ceramic samples were prepared to experimentally investigate sub-solidus phase relations in the La₂O₃-Sm₂O₃-ZrO₂ system at 1873 K and 1673 K. No ternary compounds have been observed, while the binary La₂Zr₂O₇ and Sm₂Zr₂O₇ pyrochlore phases form a continuous solid solution La_2?xSm_xZr₂O₇ in the ternary system at the selected temperatures. X-ray diffraction and microstructure results demonstrated that the pyrochlore phase is stable in the ZrO₂-rich corner. The homogeneity range of the pyrochlore phase was carefully determined and the phase boundary of the cubic ZrO₂ (fluorite phase) which extends into the ternary system was also constructed via electron probe microanalysis. The as-obtained data were adopted to determine the mixing parameters for the pyrochlore and fluorite phases in the present thermodynamic modeling. A self-consistent database of the La₂O₃-Sm₂O₃-ZrO₂ system was accordingly established for the first time and the calculations agree well with the experimental data in the current work.     

High Transparency Nd: Y2O3 Ceramics Prepared with La2O3 and ZrO2 Additives

High transparency Nd: Y₂O₃ ceramics were prepared by vacuum sintering with La₂O₃ and ZrO₂ sintering additives. The optimum in‐line transmittance of the sintered Nd: Y₂O₃ is 80.98% at the wavelength of 1100 nm, for which the content of La₂O₃ and ZrO₂ are 10.0 and 3.0 at.%, respectively. This specimen demonstrates homogeneous microstructure with the average grain size of 8.3 μm. The mechanism of sintering with La₂O₃ and ZrO₂ aids and the optical properties was discussed. The absorption, emission cross section, and fluorescence lifetime have been estimated as 1.62 × 10^?20 cm², 5.13 × 10^?20 cm², and 232 μs, respectively. Vickers hardness and the fracture toughness were measured of 9.18 GPa and 1.03 Mpa·m^1/2, respectively. All the results indicate that Nd: Y₂O₃ transparent ceramic is a promising candidate for laser material.