The role of drying-control chemical additives on the preparation of sol-gel derived PLZT thin films

Films of Pb _x/100La _x/100(Zr _y/100Ti _z/100)_1–x/400O₃ with x=8, y=65 and z=35 (PLZT(8/65/35)) with a single perovskite structural phase were successfully prepared by using drying-control chemical additives in sol-gel processing followed by rapid thermal annealing at 600 °C for only 1 min on Si(Pt) substrates. The roles of the drying-control chemical additives ethylene glycol and formamide in the gel preparation were studied. The hysteresis loop of PLZT(8/65/35) thin film was measured. The remanent polarization and coercive field were found to be about 1.3 C cm^–2 and 15 kVcm^–1, respectively.     

Elastic properties of lanthanum aluminosilicate glasses

The elastic properties of two series of lanthanum aluminosilicate glasses (15La₂O₃-xAl₂O₃-(85−x)SiO₂ and 25La₂O₃-yAl₂O₃-(75−y)SiO₂, where x, y=15, 20, 25, 30, 35 mol%), were obtained by the ultrasonic pulse-echo technique, at room temperature. The correlation of elastic stiffness, the cross-link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of Young’s modulus, bulk modulus, shear modulus and Poisson’s ratio for our glasses are compared with those theoretically calculated values in terms of the Makishima-Mackenzie model.     

(2?x)MgO · x(MnO, FeO) · 2Al2O3 · 5SiO2 (x = 0–2) ceramic materials and heat effects of their formation

We have determined the main characteristics of ceramic materials prepared by modifying 2MgO · 2Al₂O₃ · 5SiO₂ with MnO and FeO. The formation of the ceramics was analyzed by detailed thermal analysis, X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. We have determined the heat effects of formation of Mg_{1 − x} M _x Al₂O₄ (0.25 < x < 0.75) and Mg_{2 − y} M _y Al₄Si₅O₁₈ (0.5 < y < 1.5) solid solutions with M = Mn(II) and Fe(II) and calculated the standard heats of formation of the Mg_{1 − x} M _x Al₂O₄ and Mg_{2 − y} M _y Al₄Si₅O₁₈ solid solutions.     

Dielectric relaxations in SrTiO3 doped with La2O3 and MnO2 at low temperatures

In addition to the dielectric relaxation around 170 K in the cubic structure of Sr_1–3x/2La _x TiO₃, a similar relaxation was observed at about 70 K in the tetragonal structure with an activation energy in the range 0.13–0.16 eV which increases as x in Sr_1–3x/2La _x TiO₃ varies from 0.60–3.00 at%. This relaxation is explained by Skanavi's model and is discussed in terms of thermal motions of Ti⁴⁺ between potential minima produced by lattice distortions in the tetragonal structure. In order to provide a direct evidence for the suggestion that the dielectric relaxation around 170 K in the cubic is due to thermal motions of Ti⁴⁺, dielectric properties on manganese-doped specimens, Sr_1–3x/2La _x Mn _y Ti_1–y ),O₃ with x=1.40×10^–2 and y=0.1×10^–2, were investigated because Mn⁴⁺ substitutes for Ti⁴⁺. As well as the relaxation due to Ti⁴⁺, this specimen exhibits another peak due to Mn⁴⁺ with an activation energy somewhat smaller than that of Ti⁴⁺. The activation energies and the relative intensity of these relaxation processes are explained by the difference in ionic radii of Mn⁴⁺ and Ti⁴⁺ and the difference in formation energies of a strontium vacancy adjacent to Mn⁴⁺ and that to Ti⁴⁺, which were calculated theoretically using a shell model.     

The influence of silicon on microstructure and electrical properties of La-doped BaTiO3 ceramics

BaTiO₃ positive temperature coefficient of resistance ceramics were prepared with the general composition (La_0.002Ca _x Ba_0.998–x ) (Ti_1.01–y Mn _y )O₃ ·zSiO₂ and sintered in air. The Ca content as well as the amount of doped Mn were varied ranging from 4–20 mol% and 0.02–0.04 mol%, respectively. Up to 4 mol% Si was added using a new method as well as by the classical means as solid silica. In the new method, the desired quantity of Si(OC₂O₅)₄ (Si(OEt)₄), contained in dry tetrahydrofurane (THF), was dropped under a slight stream of inert gas into the vigorously stirred aqueous slurry which was manufactured after the calcination process. The addition of Si by this technique was found to result in a homogenization of the microstructure and an improvement in electrical properties. The effect of Si on electrical properties is explained by the influence of the observed second phase on the equilibrium of Ba vacancies. The results of further variation of Ca and Mn contents are presented.     

Electrical properties of evaporated MgO-TiO2 protective layer for AC PDP

Secondary electron emission from a protective layer in AC PDP is known to be dominated by potential emission mechanism, which is sensitive to its energy band structure. Therefore, the secondary electron emission property can be modified by a change in the energy band structure of the protective layer. The addition of controlled amount of titanium oxide into the conventional magnesium oxide protective material might affect the overall voltage characteristics of panels due to the fact that TiO₂ has higher dielectric constant than MgO and that the ion radius of Ti is similar to that of Mg. The electrical properties of panels with protective layers evaporated from the starting materials with different [TiO₂/(MgO + TiO₂)] ratios were investigated. When the [TiO₂/(MgO + TiO₂)] ratios of 0.1 and 0.15 were used, the panel exhibited a sustaining voltage of 122 V, which was 16 V smaller than that of the pure MgO, without lowering its memory margin. The relative dielectric constant of Mg_2–2x Ti _x O₂ films increased with addition of TiO₂ to the pure MgO, however, it then suddenly decreased above the [TiO₂/(MgO + TiO₂)] ratio of 0.1. The surface roughness of Mg_2–2x Ti _x O₂ had a minimum when the [TiO₂/(MgO + TiO₂)] ratio in the starting materials was 0.1. The variation trends of the relative dielectric constant and the surface roughness of Mg_2–2x Ti _x O₂ films with increasing [TiO₂/(MgO + TiO₂)] ratio in the starting materials were found to be consistent with that of the voltage characteristics.     

Crystallization, microstructure development and dielectric behaviour of glass ceramics in the system [SrO · TiO2]-[2SiO2 · B2O3]-La2O3

Various glasses in the system (65 – x)[SrO · TiO₂]-(35)[2SiO₂ · B₂2O₃]-(x)La₂O₃, where x = 1,5,10 (wt%) were prepared by melting in alumina crucible (1375–1575 K). Heat treatment schedules were selected from DTA plots of respective glasses. X-ray diffraction studies of glass ceramic samples containing different concentrations of La₂O₃ revealed the formation of Sr₂B₂O₅, Sr₃Ti₂O₇ and TiO₂ (rutile) phases. The addition of La₂O₃ results in the development of well formed, elongated crystallites of different phases. Results of the dielectric behaviour demonstrate higher values of dielectric constant for some of the glass ceramic samples. This can be ascribed to the relaxation polarization at the crystal-glass interface due to conductivity differences between crystalline and glassy phases.     

Superconductivity of La2−x Sr x CuO4 with high strontium concentration by sulphur doping

The effects of sulphur substitution for oxygen on the structure and properties of nonsuperconducting La_2–x Sr _x CuO₄, where x=0.26 and 0.30, have been studied. In La_2–x Sr _x CuO _4–y -S _y , the sulphur-doped samples exhibit superconducting transition at 37–39 K and a larger Meissner effect than undoped samples. It was found that the superconductivity of La_2–x Sr _x CuO_4–y S _y is apparently determined by the value of x–y and the strontium concentration region in which La_2–x Sr _x CuO₄ shows superconductivity shifts to higher strontium concentrations with sulphur doping.     

Determination of compositional fluctuation region in solid solution of lanthanum-modified lead zirconate titanate

A method was developed to determine a compositional fluctuation region in Pb_1–y La _y (Zr _x Ti_1–x )_1–(y/4)O₃ (PLZT) solid solution in the tetragonal region. The compositional fluctuation in PLZT extends two-dimensionally on the phase diagram. The method described in this paper utilized the fact that the compositional fluctuation region extends to the composition lines whose lattice spacing corresponds to the higher or lower fluctuation limit. The fluctuation limits of the lattice spacings were estimated from X-ray diffraction analysis. This method revealed that the compositional fluctuation in PLZT is difficult to be eliminated by using a conventional dry method (mixed oxide method). The shape of the region indicated that homogenization of Zr⁴⁺ and Ti⁴⁺ was more difficult as compared with that of Pb²⁺ and La³⁺.     

Phase Equilibria and Crystal Structures of Mixed Oxides in the La-Mn-Ni-O System

The phase equilibria and crystal structures of mixed oxides in the ternary system La₂O₃-Mn₃O₄-NiO are studied at 1100°C in air. The projection of the La-Mn-Ni-O phase diagram at 1100°C and = 0.21 × 10⁵ Pa onto the metal-composition triangle is found to comprise 12 phase fields. The lattice parameters of La₂NiO₄ (sp. gr. I4/mmm), La₃Ni₂O₇ (sp. gr. Cmcm), La₄Ni₃O₁₀ (sp. gr. Cmca), and La_{1 + x} Mn_{1 − x − y} Ni_yO₃ solid solutions (sp. gr. Pnma, −0.04 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.4) are determined. The composition stability limits of La₄Ni_{3 − y} Mn_yO₁₀ solid solutions are 0 < y ≤ 0.05. With increasing Ni concentration in La_{1 + x} Mn_{1 − x − y} Ni_yO₃, the metal nonstoichiometry decreases from −0.04 ≤ x ≤ 0.05 at y = 0 to x = 0 at y = 0.4.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 841–848.Original Russian Text Copyright © 2005 by Demina, Cherepanov, Petrov, Klokova.     

Study of (Bi4−x La x ) Ti3O12 Powders and Ceramics Prepared by Sol-Gel Method

La-modified (Bi_4–x La _x )Ti₃O₁₂ (abbreviated as BLT) powders were prepared by sol-gel processing methods. The powders were characterized by differential thermal analysis (DTA) and laser-diffraction particle-size analysis. The (Bi_4–x La _x )Ti₃O₁₂ ceramics were prepared from the powders and characterized by X-ray diffraction (XRD). The results indicate that the sol-gel method can be used to prepare nanometer powder for the new types of BLT ferroelectric ceramics. The solid reaction of BLT powders occurs at 730°C approximately resulting in the growth of BLT grain. The average grain size may be varied in the range 60–500 nm, depending on the calcination temperature of the powders. The (Bi_4–x La _x )Ti₃O₁₂ ceramics prepared from the powders were polycrystalline materials with completely monoclinic (Bi_4–x La _x )Ti₃O₁₂ phase.     

Synthesis of magnetic nanocomposite MgO/MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> from Mg-Fe layered double hydroxides precursors

The present letter reported the synthesis of MgO-containing magnetic nanocomposites by calcinations of tailored hydrotalcite-like layered double hydroxides (LDHs) of the type [Mg_{1 – x – y}Fe²⁺_yFe^{3 +}_x(OH)₂]^{x +}(A)_x/2·mH₂O (y 0; A = CO₃^{2 –} or SO₄^{2 –}) precursors at 900°C for 2 h. The results indicate that calcination of LDHs gives rise to the formation of magnetic nanocomposites of MgO and MgFe₂O₄ spinel ferrite, where MgO formed could disperse and separate MgFe₂O₄ particles, and MgO itself was also dispersed or embedded uniformly in the MgFe₂O₄ spinel matrix. Furthermore, initial studies on the bactericidal properties with staphylococcus aureus show that these as-synthesized nanometer-sized materials have significant bactericidal effect, which increases with the increasing volume fraction of MgO.     

Incorporation of bismuth into Ba6− x R8+2/3x Ti18O54(R = Nd, Gd)

Microstructural investigations and microanalyses of a series of Ba_6–x R _8+2/3x Ti₁₈O₅₄ ceramics (R = Nd, Gd) revealed that the solid-solubility limit for the isovalent substitution of R ³⁺ by Bi³⁺ depends on the composition of the Ba_6–x R _8+2/3x Ti₁₈O₅₄ phase. For the Nd analogue the solid-solubility limit (y in Ba_6–x (Nd_1–y Bi _y )_8+2/3x Ti₁₈O₅₄) decreases with a decrease in x from y = 0.16 for x = 2.0 to y = 0.10 for x = 0.8. An even lower solid-solubility limit (y = 0.06) was found for the Ba_4.5(Gd_1–y Bi _y )₉Ti₁₈O₅₄ compound (x = 1.5). All substituted Nd compositions exhibit higher permittivities (93–99), lower temperature coefficients of permittivity (11–15 ppm/K) and higher dielectric losses (Q · f = 1300–5500 GHz) than the parent compositions. By exceeding the solid-solubility limit, abrupt changes in the microstructural and dielectric characteristics are induced.     

Ordering of Cubic Titanium Monoxide into Monoclinic Ti5O5

The structures of ordered and disordered cubic Ti _x O _z = TiO _y (y= z/x) phases containing both Ti and O vacancies were studied by x-ray diffraction. The results demonstrate that annealing TiO _y with y= 0.9–1.1 below 1300 K leads to the formation of a monoclinic ordered Ti₅O₅phase (sp. gr. C2/m(A12m/1)). Symmetry analysis of the monoclinic Ti₅O₅superstructure indicates that the TiO _y –Ti₅O₅ordering transition is defined by the {k ₁₀} Lifshits and {k ₄} and {k ₁} non-Lifshits wavevector manifolds. The ordering is shown to be a first-order transition accompanied by a decrease in the unit-cell volume of the parent lattice. The Ti and O distribution functions in titanium monoxide are calculated, and the Ti- and O-site near-neighbor environments in the monoclinic Ti₅O₅superstructure are identified. The region of possible long-range-order parameters is outlined.     

Study of interfacial reactions in ionized metal plasma (IMP) deposited Al-0.5%wtCu/Ti/SiO2/Si structure

Interfacial reactions in Al-0.5%wtCu/Ti/SiO₂/Si structure have been investigated up to the annealing temperature of 600°C for 30 min in Argon ambient. Annealing temperature at above 500°C, Al alloy and Ti start to react and produce Al₃Ti, which was already reported. Annealing at higher temperatures (550°C, and 600°C) made Al₃Ti transformed into Al₅Ti₂, which is thermodynamically more stable than Al₃Ti. The unreacted 52 nm thick Ti which existed underneath of Al₅Ti₂ might lead to retardation of the reaction between Al₅Ti₂ and the underlying SiO₂. Hence, the formation of ternary compound (Al _x Ti _y Si _z ) which is believed to be detrimental to the contact metallization layers was protected.     

Thermoelectric Power of Al Doped La–Sr–Cu–O System

The normal-state transport properties of La_1.85–x Sr_0.15+x Cu_1–x Al _x O_y system have been investigated by means of resistivity and thermoelectric power. The structural analysis indicates that with the increase of x, both the lattice parameter a and c decrease. An MI transition appears with Al doping. Al doping partly perturb the periodic potential of the system, thus producing a weakly temperature dependent TEP. The different effect of doping between Al and other transition metal is discussed.     

Dielectric and Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3–Pb(Mg1/2W1/2)O3 Ceramics

Data are presented on the phase composition, crystal structure, microstructure, and dielectric and piezoelectric properties of (1 – y)[(1 – x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃]–yPb(Mg_1/2W_1/2)O₃ (x = 0.30–0.36; y = 0, 0.05, 0.10) ceramics. It is shown that the use of fine-particle magnesia as a starting reagent ensures the formation of single-phase materials. The ceramics with a rhombohedral structure are found to exhibit relaxor behavior. Increasing the content of the Pb(Mg_1/2W_1/2)O₃ perovskite leads to ordering of the domain structure of poled ceramics and increases their piezoelectric charge coefficient d ₃₁ and the width of their phase transitions.     

Effect of Ca Substitution on the Superconductivity of La2.5Y0.5CaBa3(Cu0.88Fe0.12)7Oz

The structural and superconducting properties of single-phase La_2.5–y Y_0.5Ca_1+y Ba₃ (Cu_0.88Fe_0.12)₇O _z (LYCaBCuFe) (y= 0.0–1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T _c ^R=0 shows a marginal increase from 31 K to 37 K for y = 0.0–0.21 and thereafter it decreases with increasing y leading to zero T _c ^R=0 at y 0.84. This shows that the suppression of T _c from 80 K to 31 K by Fe doping at x = 0.12 La_2.5Y_0.5CaBa₃(Cu_1–x Fe _x )₇O _z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.     

The effect of rare-earth oxides on the crystallization of CaO–Al2O3–SiO2 glasses

CaO–Al₂O₃–SiO₂ –La₂O₃–Nd₂O₃ glass was prepared and their physical properties, such as density, glass transition temperature and crystallization temperature, were measured. The heat treatment of these glasses precipitated Ca₂La₈(SiO₄)₆O₂ oxyapatite (CLS) crystal for 20CaO–10Al₂O₃–60SiO₂–10La₂O₃ (mol%) glass and Ca₂Nd₈(SiO₄)₆O₂ oxyapatite (CNS) crystal was precipitated with Nd₂O₃ substitution. Crystallization of these glasses was observed at the surface and internally within the samples. The spherical and stick-like crystals were observed throughout the bulk of the glasses and the surface crystal layer of oxyapatite crystals were strongly oriented along the c-axis. The apparent activation energies of crystal growth were estimated as 360 kJ mol^–1.     

Study of barium feldspar polymorphism as a function of temperature and calcium content

A family of new glass-ceramic materials, of the general formula (25-x)CaO·xBaO·yMgO· zAl₂O₃·50SiO₂, where x = 1, 2, 5, 10, 15, 20, 25, y = 20 or 14 and z = 5 or 11 (mol%), has been prepared by melting raw materials in two parent glasses and performing heat treatments. The systematic substitution of BaO for CaO in the base glasses allows the effect of feldspars' isomorphism and polymorphism to be studied in a series of glass-ceramics where the structural environment around the bivalent cations, Ca²⁺ and Ba²⁺, is systematically altered. Ba²⁺ has a large effect on the glass transition temperature and dilatometric softening point, causing a decrease with increasing BaO. The crystalline phases have been identified and found to be dependent on the preparation conditions, which are the BaO and Al₂O₃ contents, the heating rate and the soaking temperature adopted for the crystallization treatments. The infrared spectroscopy technique helped to identify the different polymorphs of barium feldspar, that were not clearly distinguishable by X-ray powder diffractometry due to preferred orientations. The kinetic parameters for the formation of the different crystals have also been determined and correlated with their thermal stability resumed in the well-known time-temperature-transformation curves.