Microstructure Characterization of the (1−x)La2/3TiO3·xLaAlO3 System

Microstructural characterizations on the (1− x )La_2/3TiO₃· x LaAlO₃ (LTLA) system were conducted using transmission electron microscopy. The presence of La₂Ti₂O₇ and La₄Ti₉O₂₄ phases in pure La_2/3TiO₃ is confirmed by the electron diffraction pattern. When x = 0.1, the ordering due to the A-site vacancies could be confirmed by the presence of antiphase boundaries (APBs) and return ½(100) superlattice reflection. As x increases, the ordering decreases and finally disappears when x = 0.6. The tilting of oxygen octahedra could be demonstrated by the presence of the ferroelastic domains in the matrix and return ½(111) and return ½(110) superlattice reflections in selected area electron diffraction patterns. In pure LaAlO₃, only the antiphase tilting of oxygen octahedra is present due to the presence of return ½(111) superlattice reflection. In the LTLA system of x = 0.1, both the antiphase and in-phase tiltings of the oxygen octahedra are involved; however, in the range of x from 0.3 to 0.9, the antiphase tilting of oxygen octahedra has appeared. The growth of the ferroelastic domains is influenced by the APBs in the matrix.     

Vaporization Studies of the La2O3–Ga2O3 System

The vaporization of the samples of the compositions Ga₂O₃+ LaGaO₃, LaGaO₃+ La₄Ga₂O₉, and La₄Ga₂O₉+ La₂O₃ was investigated using Knudsen effusion mass spectrometry in the temperature range 1494–1937 K. The partial pressures of the gaseous species O₂, Ga, GaO, Ga₂O, and LaO were determined over the samples investigated. The equilibrium partial pressures were used for the calculation of the thermodynamic activities of the components at 1700 K. Gibbs energies of formation of LaGaO₃( s ) and La₄Ga₂O₉( s ) at 1700 K from the component oxides were derived from the thermodynamic activities as −46.4 ± 4.7 and −99.2 ± 7.9 kJ·mol⁻¹, respectively. The results were compared with the literature data obtained using other methods.     

Low-Temperature Synthesis and Properties of LaMnO3±d and La0.67R0.33MnO3±d (R = Ca, Sr, Ba) from Citrate Precursors

LaMn_{1− y} ³⁺Mn _y ⁴⁺O_3±d and La_0.67R_0.33Mn_{1− y} ³⁺Mn _y ⁴⁺O_3±d (R = Ca, Sr, Ba) phases were synthesized at 350°C by using very reactive, amorphous precursors obtained from the stoichiometric citrate solutions. The chemical process was optimized with respect to the solution concentration, pH, and additives. The precursor reactions were investigated as a function of the cation stoichiometry and the additive by simultaneous thermal and thermogravimetric analysis and X-ray diffraction. The reaction pathway was found to be independent of the cation stoichiometry, but related to the acid or base additive. The annealing temperature was systematically increased in the 350–1200°C interval and the La_0.67Sr_0.33MnO_3±d properties (i.e., crystal sizes, Mn average valence, Curie temperature, magnetization, magnetic susceptibility) were measured and found to vary consistently as a function of it.     

Crystal Structure Refinement of La0.683(Ti0.95Al0.05)O3 Perovskite by the Rietveld Method

The structural parameters of orthorhombic and tetragonal phases (space group P / mmm and P 4/ mmm ) of A-site deficient La_0.683(Ti_0.95Al_0.05)O₃ perovskite have been refined by Rietveld analysis through the X-ray powder diffraction patterns measured in the temperature range from 15° to 500°C. With an increase in temperature the unit-cell parameters a , b , and c increased, while the b / a ratio decreased and became unity between 200° and 400°C. No significant changes were observed for atomic coordinates throughout the temperature studied. These results strongly suggest that the phase transition is induced by lattice distortion.     

Piezoelectric Properties of (1−x)(Na0.5K0.5)NbO3–xAgSbO3 Lead-Free Ceramics

(1− x )(Na_0.5K_0.5)NbO₃– x AgSbO₃ lead-free piezoelectric ceramics were prepared by normal sintering. The effects of the AgSbO₃ on the phase structure and piezoelectric properties of the ceramics were systematically studied. These results show that the AgSbO₃-modified (K_0.50Na_0.50)NbO₃ lead-free piezoelectric ceramics form stable solution with orthorhombic structure, and the Curie temperature and the polymorphic phase transition of the ceramics decreased with increasing AgSbO₃. The result shows that the piezoelectric properties of the ceramics strongly depend on the AgSbO₃. The ceramics with x =0.05 possess optimum properties ( d ₃₃=192 pC/N, k _p=43%, T _c=348°C, T _o−t =145°C, ɛ_r∼632, and tan δ∼3.5%). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.     

Microstructure and Piezoelectric Properties of (1−x)(Na0.5K0.5)NbO3–xLiNbO3 Ceramics

(1− x )(Na_0.5K_0.5)NbO₃– x LiNbO₃ [(1− x )NKN– x LN] ceramics were produced by the conventional solid-state sintering method, and their microstructure and piezoelectric properties were investigated. The formation of the liquid phase and K₆Li₄Nb₁₀O₃₀ second phase that were observed in the (1− x )NKN– x LN ceramics was explained by the evaporation of Na₂O during the sintering. A morphotropic phase boundary (MPB) was observed in the specimens with 0.05< x <0.08. Promising piezoelectric properties were obtained for the specimens with x =0.07. Therefore, the piezoelectric properties of this 0.93NKN–0.07LN ceramic were further investigated and were found to be influenced by their relative density and grain size. In particular, grain size considerably affected the d ₃₃ value. Two-step sintering was conducted at different temperatures to increase the grain size. Piezoelectric properties of d ₃₃=240 (pC/N) and k _p=0.35 were obtained for the 0.93NKN–0.07LN ceramics sintered at 1030°C and subsequently annealed at 1050°C.     

Metal Propionate Synthesis of Magnetoresistive La1−x(Ca,Sr)xMnO3 Thin Films

A flexible chemical solution deposition (CSD) method for the preparation of magnetoresistive La_1−x (Ca,Sr)x MnO₃thin films based completely on metal propionates is pre-sented.A number of polycrystalline thin films with varying stoichiometries were deposited on different substrate ma-terials at temperatures between 550° and 850°C. The crys-tallization behavior on selected substrates was found to de-pend on the thin film stoichiometry. Magnetoresistivity and magnetization were measured as a function of temperature. For the selected samples, a magnetic Curie temperature TC, a metal–semiconductor transition, and magnetoresistive behavior were observed. These measurements demon-strated that La_1−x(Ca,Sr)x MnO₃ thin films with properties well known from films deposited by PLD or sputtering can be prepared by a simple, propionate-based CSD method.     

Structure and Electrical Properties of A-site-Deficient Perovskite Compounds in the La2/3TiO3-La1/3NbO3 System

The structure and electrical properties of an A-site-deficient perovskite compound found in the La_2/3TiO₃-La_1/3NbO₃ system were investigated. The composition of the perovskite compound seemed to be very close to La_0.633(Ti_0.90Nb_0.10)O₃. X-ray diffraction analysis revealed a superstructure with a doubled c -axis parameter, resulting from an ordered arrangement of the A-site cation vacancies. Impedance measurements on the compound showed that La_0.633(Ti_0.90Nb_0.10)O₃ had high ionic conductivity at relatively low temperature (<770 K) and increased electronic conduction at high temperature (>770 K). The bulk ionic conductivity was comparable with that of La_0.683(Ti_0.95Al_0.05)O₃, which has the highest ionic conductivity among the La-(Ti,Al)-O perovskite compounds.     

Lanthanum-Modified (1 – x)(Bi0.8La0.2)(Ga0.05Fe0.95)O3·xPbTiO3 Crystalline Solutions: Novel Morphotropic Phase-Boundary Lead-Reduced Piezoelectrics

(1 – x )(Bi_0.8La_0.2)(Ga_0.05Fe_0.95)O₃· x PbTiO₃ (BLGF-PT) crystalline solutions have been fabricated by solid-state reactions. BLGF-PT has single perovskite phase structure with a rhombohedral–tetragonal (FE_r-FE_t) morphotropic phase boundary (MPB) at a PT content of x = 0.43. Lanthanum substitution has been found to increase the insulation resistance and decrease the coercive field down to 20 kV/cm, which results in significant improvements in dielectric and piezoelectric properties of BLGF-PT. The dielectric constant, loss tangent, Curie temperature, remnant polarization, piezoelectric d ₃₃ constant, and planar coupling factor of 1760, 0.05, 264°C, 33 μC/cm², 295 pC/N, and 0.36, respectively, have been achieved for BLFG-PT in the vicinity of the MPB. Compared with conventional Pb(Zr,Ti)O₃ (PZT) piezoelectric ceramics, the BLGF-PT is a competitive alternative piezoelectric material with decreased lead content.     

Preparation of the High-Quality Superconductor La1Ba2Cu3Oy

The relationship between the preparation procedure and superconducting properties of La₁Ba₂Cu₃O_y was studied. A series of samples was sintered in an N₂-gas atmosphere for various lengths of time ranging from 1 to 40 h, followed by a fixed annealing procedure in O₂. It was found that the shorter the sintering period, the higher was the oxygen content. The samples sintered for a period of less than 15 h contained excess oxygen compared with La₁Ba₂Cu₃O₇ and exhibited poor superconducting properties. The sample sintered for 40 h had an oxygen content y equal to 6.95, and had excellent superconducting properties. The mechanism for preparing high-quality La₁Ba₂Cu₃O_y is discussed.     

Lithium Ion-Conducting Glass–Ceramics of Li1.5Al0.5Ge1.5(PO4)3–xLi2O (x=0.0–0.20) with Good Electrical and Electrochemical Properties

NASICON-type structured Li_1.5Al_0.5Ge_1.5(PO₄)₃– x Li₂O Li-ion-conducting glass–ceramics were successfully prepared from as-prepared glasses. The differential scanning calorimetry, X-ray diffraction, nuclear magnetic resonance, and field emission scanning electron microscope results reveal that the excess Li₂O is not only incorporated into the crystal lattice of the NASICON-type structure but also exists as a secondary phase and acts as a nucleating agent to considerably promote the crystallization of the as-prepared glasses during heat treatment, leading to an improvement in the connection between the glass–ceramic grains and hence a dense microstructure with a uniform grain size. These beneficial effects enhance both the bulk and total ionic conductivities at room temperature, which reach 1.18 × 10⁻³ and 7.25 × 10⁻⁴ S/cm, respectively. In addition, the Li_1.5Al_0.5Ge_1.5(PO₄)₃–0.05Li₂O glass–ceramics display favorable electrochemical stability against lithium metal with an electrochemical window of about 6 V. The high ionic conductivity, good electrochemical stability, and wide electrochemical window of LAGP–0.05LO glass–ceramics suggest that they are promising solid-state electrolytes for all solid-state lithium batteries with high power density.     

Structure Evolution from Pb(Mg1/3Nb2/3)O3 to La(Mg2/3Nb1/3)O3

The crystal structure of lanthanum-modified lead magnesium niobates having composition (Pb_{1− x} La _x ) (Mg_{(1+ x )/3}-Nb_{(2− x )/3})O₃ with X = 0 to 1 was investigated by X-ray powder diffraction. It was found that the fundamental reflections from perovskite structure remain in the whole range of composition. The superlattice reflections from the A(B'_1/2-B"_1/2)O₃ ordered structure are also well preserved for La content greater than 50 at.%; however, a series of extra peaks of mixing indices appears, with intensities gradually enhanced with the increase of La content. For the complete substitution of Pb by La, a splitting of some reflections can be observed in the diffraction pattern. The results indicate that the crystal structure evolves continuously with the La content, from disordered cubic perovskite of space group Pm 3 m for X = 0, to ordered cubic perovskite of space group Fm 3 m for X = 0.5, distorted cubic perovskite of space group Pa 3 for 0.5 < X < 0.9, and finally to a rhombohedral perovskite, possibly belonging to the space group R 3 , for X ≥ 0.9. In the evolution of structure, a linear reduction of the lattice constant of the perovskite cell from 4.048 to 3.964 Å was observed.     

Low-Temperature Densification of Lanthanum Strontium Manganite (La1−xSrxMnO3+δ), x=0.0–0.20

Intermediate-stage sintering of lanthanum strontium manganite (LSM, where Sr=0.00, 0.05, 0.10, 0.15, and 0.20) was shown in dilatometry studies to be accelerated when subjected to alternating flows of air and nitrogen. The extent of rate enhancement decreased with increased Sr content, and decreased with increased temperature, which coincides with diminished oxygen nonstoichiometry. Shrinkage rates were further shown to be sensitive to the difference in oxygen content in the alternating gas flows. Baseline air sintering rates were measured using stepwise isothermal dilatometry, from which kinetic parameters were calculated using the Makipirtti–Meng model. Activation energies for sintering in air were determined to be 255 ± 26, 258 ± 28, 308 ± 32, 373 ± 37, and 417 ± 41 kJ/mol for Sr=0.0, 0.05, 0.10, 0.15, and 0.20, respectively. A diffusion-based model is proposed that is consistent with trends in accelerated shrinkage versus temperature. Transient cation vacancy gradients, which lead to higher cation mobility, were calculated from established oxygen diffusivities and oxygen nonstoichiometry as a function of temperature and time. A potential application of this approach is the processing of LSM-based cathode-side contact pastes in solid oxide fuel cells.     

Chemical Solution Deposition of Transparent and Metallic La0.5Sr0.5TiO3+x/2 Films Using Topotactic Reduction

Metallic and transparent La_0.5Sr_0.5TiO_{3+ x /2} films were prepared by the chemical solution deposition (CSD) method using topotactic reduction processing. The use of Si powder as the reducing agent was facile and allowed easy manipulation. It was observed that metallic (resistivity at 300 K ∼2.43 mΩ cm) and transparent (∼80% transmittance at visible light) La_0.5Sr_0.5TiO_{3+ x /2} films could be obtained with an annealing temperature of 900°C, which was significantly lower than the hydrogen reduction temperature (∼1400°C). The successful preparation of metallic and transparent La_0.5Sr_0.5TiO_{3+ x /2} films using CSD has provided a feasible route for depositing other perovskite-structured functional layers on La_0.5Sr_0.5TiO_{3+ x /2} films using this low-cost all CSD method.     

Characterization of Flux-Grown Ca(WO4)x(MoO4)1–x Crystals

Crystals of Ca(WO₄) _x (MoO₄)1– x , in the range x =0.072 to 0.86 were successfully grown by the flux technique. Neither the densities of the mixed crystals nor the cell parameters vary linearly. The dislocation density of the mixed crystals, determined by the etching technique, is greater than that of the end partners. The variation in microhardness of the mixed configurations is found to be linear and has no correlation with their dislocation content.     

Microwave Dielectrics in the (La1/2Na1/2)TiO3–Ca(Fe1/2Nb1/2)O3 System

Dielectric properties of the system (1 − x)(La_1/2Na_1/2)TiO₃– _x Ca(Fe_1/2Nb_1/2)O₃, where 0.4 # x # 0.6, have been investigated at microwave frequencies. The temperature coefficient of resonant frequency (τ_f), nearly 0 ppm/°C, was realized at x = 0.58. These ceramics had perovskite structure and showed relatively low dielectric losses. A new dielectric material applicable to microwave devices having Q · f of 12000–14000 GHz and a dielectric constant (ε_r) of 59–60 has been obtained at 1300–1350°C for 5–15 h sintering.     

Structure and Magnetic Properties of La0.7Ca0.3MnO3−δ for (3 −δ) < 3.0

Annealing studies were conducted on bulk La_0.7Ca_0.3MnO_3−δ to determine the sensitivity of its structural and magnetic properties to oxygenation conditions. Standard bulk sintering conditions, thin-film annealing conditions for obtaining good magnetoresistive properties, and a reducing anneal, which corresponded to the onset of phase decomposition, were conducted. The main phase formed was a face-centered (fcc) pseudocubic double-perovskite structure, with cell parameters of a ∼ 2 a _p∼ 0.772 nm, where a _p is the single-perovskite cubic cell parameter. A minor superstructure—body-centered pseudotetragonal, with lattice parameters of c = 4 a _p and a =√2 a _p—was observed in samples with (3 −δ) < 3. A maximum of 20% of the superstructure was formed using the most-reducing conditions. The superstructure had a lower critical temperature than the main phase and depressed ferromagnetic order.     

Phase Transitional Behavior and Piezoelectric Properties of Lead-Free (Na0.5K0.5)NbO3–(Bi0.5K0.5)TiO3 Ceramics

(1− x )(Na_0.5K_0.5)NbO₃–(Bi_0.5K_0.5)TiO₃ solid solution ceramics were successfully fabricated, exhibiting a continuous phase transition with changing x at room temperature from orthorhombic, to tetragonal, to cubic, and finally to tetragonal symmetries. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was found at 2–3 mol% (Bi_0.5K_0.5)TiO₃ (BKT), which brings about enhanced piezoelectric and electromechanical properties of piezoelectric constant d ₃₃=192 pC/N and planar electromechanical coupling coefficient k _p=45%. The MPB composition has a Curie temperature of 370°–380°C, comparable with that of the widely used PZT materials. These results demonstrate that this system is a promising lead-free piezoelectric candidate material.     

Preparation and Aging Behavior of Chemical-Solution-Deposited (Pb(Mg1/3Nb2/3)O3)1-x–(PbTiO3)x Thin Films without Seeding Layers

The aging behavior of the solid-solution series (Pb(Mg_1/3Nb_2/3)O₃)_{1− x} –(PbTiO₃) _x (PMN_{1− x} −PT _x ) prepared by chemical-solution deposition without seeding layers was investigated. A strong influence of the rapid thermal annealing step on the film density was determined. The best nucleation and density of the thin films occurred when each deposited layer was separately pyrolyzed and crystallized. The thin-film microstructure was investigated using scanning electron microscopy. Conventional capacitance-voltage and hysteresis measurements were performed. For the first time, investigations on the fatigue performance and the leakage current for alternating-current and direct-current voltage were executed, which are important for the reliability in device applications.     

New Phases in the CaO–M2O3–CuO (M = Nd, Gd, Y) Systems at 1000°C

New layered cuprates with the general stoichiometry Ca_{2+ x} M_{2− x} Cu₅O₁₀ have been characterized for M = Nd, Gd, and Y. These insulating phases have structures closely related to that of NaCuO₂ and contain one-dimensional chains constructed from edge-sharing [CuO₄] square planes. The X-ray patterns of these ternary cuprate phases are complicated by strong reflections from both incommensurate and commensurate supercells which result from the ordering of the Ca²⁺ and M³⁺ ions in the structure. The stoichiometry range, and resultant Cu valences in these cuprates depend upon the nature of the trivalent ion. Ca-rich and trivalentrich compositions can be prepared for M = Nd and Gd, but only Ca-rich compositions were formed in the Y system. No other ternary phases are observed under the conditions of this study, 1000°C in air, and the solid-state equilibria are dominated by the single ternary phase identified above.