Na3Zr2-xInxSi2-xP1+xO12系统的组成、结构和离子电导的关系

用固相反应、X射线衍射、金相显微镜观察、测定比热和复平面阻抗谱的方法研究了Na₃Zr_2-xIn_xSi_2-xP_1+xO₁₂系统。在此系统中存在两种固溶体:单斜固溶体(0≤x<0.8)和三方固溶体(0.8≤x≤1.8)。即从x=0.8的组成开始,NASICON型Na₃Zr_2-xIn_xSi_2-x 关键词：     

Raman scattering from CaxZr1−xO2−x阳x,a system with massive point defects

Raman spectra have been measured on a series of solid solutions in the system ZrO₂-CaO at compositions consisting of a two-phase mixture of monoclinic ZrO₂ and calcium-saturated cubic ZrO₂ and of single-phase fluorite structure Ca_xZr_?xO_2?x阳_x. It is shown that introduction of translational disorder through random substitution of Ca²⁺ cations and anion vacancies leads to complete breakdown of selection rules and the production of a spectrum that essentially represents the frequency distribution of the density of states in agreement with theoretical predictions.     

Phase relation in the BaO-ZrO2-YO1.5 system: Presence of separate BaZrO3 phases and complexity in phase formation

In order to estimate the phase stability and homogeneous range of BaZrO₃, which is expected as a candidate electrolyte material for intermediate temperature solid oxide fuel cell, the phase relation in the BaO-ZrO₂-YO_1.5 systems has been examined at a typical processing temperature of 1600 °C. The stable existence of two cubic phases of BaZrO₃, termed as BZ(I) and BZ(II), with different dopant concentration is observed above 1400 °C in the present study. The latter is of long-range ordered supercell with a wide range of solid solution between Ba₃Zr₂YO_8.5 and Ba₉Zr₄Y₈O₂₉. Also observed is the presence of liquid phase at higher BaO concentration region above the ternary eutectic temperature that is estimated to be around 1300 °C, giving enormous effects to sintering process when Y³⁺ is overdoped beyond the solubility limit. From the present results, the pseudo-ternary phase diagram of BaO-ZrO₂-YO_1.5 of the isothermal section at 1600 °C is proposed.     

Phase diagrams of the CoMnO system in air

A retrospective critical analysis of phase diagrams of the CoMnO system in air has been made. A high-temperature phase equilibrium of the CoMnO system in air and phase diagrams of this system under different cooling conditions (quenching in water, quenching in air, cooling at rate of 25°K h^?1) have been constructed. A comparative analysis of these diagrams shows that whatever the cooling rate, cooling does not preserve the high-temperature state of the system and is accompanied (depending on cooling conditions, temperature and Co/Mn ratio) by one or more of the following phenomena: (1) oxidation of the Co_NMn_1?NO solution to spinel-type solid solutions (2) merging of a cubic and tetragonal spinel phase and formation of a homogeneous tetragonally distorted spinel (3) tetragonal distortion of the spinel lattice (4) decomposition of the cubic spinel into a cubic and tetragonal spinel. (5) decomposition of the cubic spinel into a cubic, tetragonal and slightly distorted tetragonal spinel. Therefore, the form of the phase diagram of the CoMnO system in air is entirely determined by the method of cooling.     

Synthesis and physical properties of negative thermal expansion materials Zr1−xMxW2O8−y (M=Sc, In, Y) substituted for Zr(IV) sites by M(III) ions

Zr_1−xM_xW₂O_8−y (M=Sc, In and Y) solid solutions substituted up to x=0.04 for Zr(IV) sites by M(III) ions were synthesized by a solid-state reaction. X-ray diffraction experiments from 90 to 560 K revealed that all solid solutions had a cubic crystal structure and showed negative thermal expansion coefficients. The lattice parameters of Zr_1−xM_xW₂O_8−y were smaller than that of ZrW₂O₈ probably due to oxygen defects, though the ionic radii of substituted M³⁺ ions were larger than that of Zr⁴⁺. Order-disorder phase transition temperatures of the substituted samples drastically decreased in the order of Y, In and Sc compared to the percolation theory, and decreased with increasing M content.     

Effect of chemical modification on the structure and dielectric and magnetic properties of multiferroic (1 – x)BiFeO3-xDyFeO3 solid solution

The solid solution of (1-x)BiFeO₃-xDyFeO₃ was prepared by solid state reactions in the form of ceramics. The effects of chemical modification by means of aliovalent ionic substitution of Ti⁴⁺ for Fe³⁺ on the structure and dielectric properties were investigated. A morphotropic phase boundary bridging the perovskite rhombohedral phase and the orthoferrite orthorhombic phase was identified at x around 0.1. The chemical modification was found to stabilize the perovsite phase. The dielectric performance of the solid solution was improved by the substitution of Ti⁴⁺ for Fe³⁺, which decreased the electric conductivity by reducing oxygen vacancies, as evidenced by the decrease in loss tangent values. Magnetic hysteresis and large saturated magnetization (0.5 μ_B/f.u.) were realized in 0.92BiFeO₃-0.08DyFeO₃ with 2% substitution of Ti⁴⁺ for Fe³⁺, which is believed to arise from the disruption of the spiral spin modulation after structural modification, and the interaction between the spins of the Dy³⁺ and Fe³⁺ at low temperatures which decouples the antiferromagnetic order between the Fe³⁺ ions.     

On the structural stability and oxygen permeation behavior of inorganic SrCo0.8Fe0.2O3−δ membranes

The high oxygen permeability combined with reasonable structural stability of perovskite-type ABO_3−δ compounds is vital for their potential applications in gas separation, solid oxide fuel cells, sensors, etc. Hence, an attempt is made to develop SrCo_0.8Fe_0.2O_3−δ-based dense membranes with sol-gel-derived oxalates and study their phase stability and oxygen permeation. While X-ray diffraction confirms the presence of a perovskite-type cubic phase above 800 °C, X-ray photoelectron spectroscopy reveals the presence of cobalt and iron in 3+ and 4+ oxidation states with O₂ ²⁻, O₂ ⁻ and O⁻ species. The electrical conductivity increases up to a characteristic temperature and decreases slowly thereafter via pronounced carrier scattering. A 1.5-mm-thick membrane displays reasonable oxygen permeability of 1.05 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C but has inadequate stability. Partial substitution of iron with zirconium is shown to improve permeability and stability significantly. Thus, SrCo_0.8Fe_0.15Zr_0.05O_3−δ membrane shows promise for oxygen permeation purposes.

     

Optical, structural and fluorescence properties of nanocrystalline cubic or monoclinic Eu:Lu2O3 films prepared by pulsed laser deposition

Eu³⁺-doped lutetium oxide (Eu:Lu₂O₃) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 °C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu³⁺ fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band.     

Characterization of ceria-yttria stabilized zirconia plasma-sprayed coatings

Ceria-yttria stabilized zirconia (CYSZ) coatings were prepared by air plasma-sprayed on the nickel alloy. The as-sprayed CYSZ coatings and heat-treated CYSZ coatings were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The XPS data indicated the coexistence of Ce³⁺, Ce⁴⁺, Y³⁺ and Zr⁴⁺ ions near the surface of the as-sprayed CYSZ coatings and the disappearance of Ce³⁺ ions in the CYSZ coatings after thermal treatment at 1000 °C for 15 h. From the XRD patterns, the solid solution of CeO₂-Y₂O₃-ZrO₂ formed in the CYSZ coatings because of the lack of any features from Y₂O₃ and ZrO₂ single phases. After thermal treatment, the main phases of all the samples were consistent with the characteristic peaks of cubic ZrO₂.     

57Fe,61Ni and91Zr hyperfine field distributions in magnetic Tm-Zr amorphous alloys

Pulsed NMR measurements were performed on [Tm₁ (Tm₂)]_90+x Zr_10?x (Tm=Fe, Co, Ni) amorphous alloys utilizing a newly developed low temperature wide band probehead-preamplifier system. A 11,6 T broad⁵⁷Fe hyperfine field distribution around the average of 23.6 T together with a less intensive peak around 11 T has been found in Fe_90.6Zr_9.4, in excellent agreement with Mössbauer studies. A rather flat distribution around the average value of 14.8 T characterizes the transferred hyperfine field at the Zr sites in the same alloy. Both features provide strong evidence for a broad range of exchange interactions and variations in the spin density at the Fe sites in this material. A much narrower and symmetrical distribution at the Zr sites around 10 T in Co₉₀Zr₁₀ is evidence of the higher magnetic homogeneity of this alloy as compared to Fe₉₀Zr₁₀. In Fe₆₀Ni₃₀Zr₁₀, in addition to the⁵⁷Fe signal, a contribution from⁶¹Ni nuclei could be separated, corresponding to an average hyperfine field value of 15.3 T.     

Nanostructures in calcia stabilized hafnia thin films observed by PAC as a function of temperature

The hyperfine quadrupole interaction at Hf sites in films and powders of 14 mol% CaO–HfO₂ and 20 mol% CaO–HfO₂ has been determined as a function of temperature. Results indicate the formation of a cubic solid solution and other microstructures assigned to the ?₁ (CaHf₄O₉) and ?₂ (Ca₆Hf₁₉O₄₄) phases. Dynamical effects on the electric field gradient reveal the existence of oxygen vacancies movements in the solid solution. The thermal behavior of the relaxation constant observed in films allowed the determination of activation energies of 0.54 eV and 0.70 eV for the 14 mol% and 20 mol% CaO doped hafnias, respectively. The influence of the microdomains and the stability of the cubic solid solution are discussed.     

Synthesis and physicochemical properties of Li2 Me x Zr1 − x O3 − δ (Me = Nb,Ti; x = 0.05, 0.1) solid solutions

Complex lithium metallates Li₂ Me _x Zr_{1 ? x} O_{3 ? δ} (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr⁴⁺ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti⁴⁺ and Nb⁵⁺ ions in the crystal structure of Li₂ZrO₃ is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li₂Ti_0.1Zr_0.9O₃ solid solution has higher conductivity than phases of undoped lithium zirconate.     

Structure and electrical behavior in air of TiO2-doped stabilized tetragonal zirconia ceramics

2 -doped YTZP ([%mol]3 Y₂O₃) compositions sintered in the temperature range of 1300 to 1450 °C, the tetragonal zirconia solid solutions field for the ZrO₂-Y₂O₃-TiO₂ system was established. The solubility of TiO₂ in YTZP was found to be about 12–[%mol]14 at 1450 °C. Structural characterization of the Ti-YTZP tetragonal zirconia solid solutions was carried out using X-ray absorption spectroscopy (EXAFS and XANES) to provide information on the environment of Ti atoms. The electrical behavior in air of the TiO₂-doped tetragonal zirconia solid solutions was studied by impedance spectroscopy in the temperature range of 300 to 800 °C, and it was found that the ionic conductivity decreases with increasing titania content. EXAFS and XANES results show that as the Ti⁴⁺ ions dissolve into the tetragonal zirconia YTZP matrix, a displacement of Ti ions from the center of symmetry takes place, leading to a non-random substitution of Ti⁴⁺ ions on Zr⁴⁺ lattice sites. Ti-O bond distances derived from EXAFS indicate that the Ti ion can be in a square-pyramidal arrangement, i.e., fivefold oxygen-coordinated. As a consequence two kinds of cation–oxygen vacancy associations are created; the high-mobility oxygen-vacancy–eightfold-coordinated cation (Zr⁴⁺) and the low-mobility oxygen-vacancy–fivefold-coordinated cation (Ti⁴⁺). This results in a decrease in the global concentration of moving oxygen vacancies and, therefore, in a decrease of the electrical conductivity. Received: 1 April 1998/Accepted: 28 September 1998     

Electrical conductivity and structure of CaO-stabilized zirconia doped with copper and iron

The investigation of the influence of copper and iron oxides on the electrical conductivity, the lattice defects and the structure of calcia-stabilized zirconia has shown that (i) the influence of copper is negligible due to the evaporation of this element at the sintering temperature as a consequence of its high volatility; (ii) the presence of iron in the sample prevents sintering of the calcia-stabilized zirconia; (iii) the addition of iron causes decomposition of the cubic solid solution Ca_xZr_1?xO_2?x into monoclinic ZrO₂, the vacant phase Ca_0.1Zr_0.9O_1.9, calcium ferrite and iron oxides; the solubility limit of iron oxide was found to be ≈1 mol%; (iv) the calcia-stabilized zirconia doped with iron is a mixed conductor at low temperatures; at high temperatures (>1073 K) it is a dominant ionic conductor.     

Exploring the morphotropic phase boundary in copper(II)-modified Pb[Zr0.54Ti0.46]O3 ferroelectrics

Copper(II)-doped Pb[Zr_0.54Ti_0.46]O₃ (PZT) ferroelectrics with a dopant concentration of 0.25 mol% were investigated at high magnetic fields, enabling an enhanced resolution of the structural distortion at the dopant site. The results obtained suggest that Cu²⁺ substitutes as an acceptor centre for [Zr,Ti]⁴⁺ in oxygen octahedra with tetragonal, monoclinic and rhombohedral distortion, confirming the model of mesoscopic mixing at the morphotropic phase boundary. PACS 61.72.Ji; 61.72.Ww; 76.30.Fc; 77.80.Bh; 77.84.Dy     

Preparation and electrical properties of a pyrochlore-related Ce2Zr2O8−x phase

A pyrochlore-related Ce₂Zr₂O_8−x phase has been prepared in a reduction reoxidation process from Ce_0.5Zr_0.5O₂ powders. Ce₂Zr₂O_8−x, based on a cubic symmetry with a=1.053 nm, decomposes in nitrogen at 800 °C, but remains stable up to 900 °C in air. It shows mixed oxygen ionic and electronic conductivity. The bulk conductivity at 700 °C is 4×10⁻⁴ S cm⁻¹ in air and 1×10⁻² S cm⁻¹ in nitrogen, and the activation energy is 1.27 eV in air. In nitrogen, the Arrhenius law is not obeyed, and a curved plot was obtained from 400 to 700 °C; then, the conductivity decreased rapidly due to the thermal decomposition of Ce₂Zr₂O_8−x.     

Theoretical Study of Antiferrodistortive Phase Transition in Strontium Titanate

SrTiO₃在105 K发生反铁畸变从立方相进入四方相,这是由氧八面体绕一晶轴转动一微小角度引起的. 根据居里原理分析其序参量是一个三阶全对称的极张量. 从吉布斯自由能出发,得到了考虑量子效应的介电常数,并分析了低温时的居里-外斯行为. SrTiO₃的低温介电行为与Sr²⁺的离子半径小有关,与BaTiO₃和PbTiO₃中的Ba²⁺和Pb²⁺相比,Sr²⁺更容易在氧八面体孔道中移动.     

Mössbauer study of the crystallization products of a Fe75Zr25 amorphous alloy

The crystallization of the Fe₇₅Zr₂₅ as-milled amorphous alloy has been studied by Mössbauer spectroscopy. The process begins at around 880 K with the complete and fast crystallization of the amorphous phase into the crystalline α-Fe and Fe₂Zr ones but, from around 915 K, there is a sudden phase transformation into the Fe₂₃Zr₆ phase, which remains stable after cooling. A fitting for the Mössbauer contribution of the Fe₂₃Zr₆ phase, consistent with its crystalline structural features, has been obtained.     

Crystal structure and photoluminescence correlations in white emitting nanocrystalline ZrO2:Eu3+ phosphor: Effect of doping and annealing

White emitting nanocrystalline ZrO₂:Eu³⁺ phosphors were synthesized by a simple precipitation route without using a capping agent. X-ray diffraction (XRD) study of ZrO₂ and ZrO₂:Eu³⁺samples revealed the presence of monoclinic and tetragonal phases. The monoclinic phase increases with increase in the annealing temperature while the tetragonal phase increases with increase in the concentration of Eu³⁺. This can be attributed to the presence of oxygen vacancy evolved when Zr⁴⁺ is replaced by Eu³⁺. Photoluminescence (PL) emission peaks of Eu³⁺ are observed at 591, 596, 606 and 613 nm on monitoring excitation wavelengths at 250, 286, 394 and 470 nm. The peaks at 591 and 606 nm were found to correlate with the tetragonal phase and those at 596 and 613 nm with the monoclinic phase. Intensities of these peaks are found to change as the crystal structure changes. The lifetime value corresponding to 591 nm peak increases with Eu³⁺ concentration at a particular heating temperature indicating increase of tetragonal phase with respect to monoclinic phase. The CIE co-ordinates of the doped samples were found to be close to that of white color (0.33, 0.33). The changes in the crystal structure of the doped samples due to doping and annealing did not affect the white color emission.     

NTCR behavior of Sm-substituted barium zirconium titanate nanocrystalline solid solution

Ceramic solid solution of nanocrystalline barium zirconium titanate in the form of Ba(Zr_0.52Ti_0.48)O₃ substituted by samarium (Sm³⁺) was prepared using the conventional solid state reaction method. The phase assemblage analyzed by the X-ray diffraction technique was fitted for cubic-crystal-symmetry. The change in the grain size depicted the influence of Sm³⁺ ions on the microstructure. The electrical behavior was studied in the temperature range from 323 to 773 K. The sintered samples exhibited a negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior above 513 K. Addition of Sm³⁺ increased the room temperature resistivity of Ba(Zr_0.52Ti_0.48)O₃ solid solution. The results obtained from the thermoelectric power measurement confirm electrons as the majority charge carriers.