Substrate effect on the properties of La<Subscript>0.775</Subscript>Sr<Subscript>0.225</Subscript>MnO<Subscript>3</Subscript> films

La_0.775Sr_0.225MnO₃ films have been produced by screen printing on various substrates (Al₂O₃, BaTi_0.85Zr_0.11Sn_0.04O₃, Ba_0.996Y_0.004TiO₃, Ba_0.996Y_0.004TiO₃ + 0.04%Mn, and Ba_0.996Y_0.004Ti_0.65Sn_0.35O₃), and their electrical properties have been studied in comparison with those of bulk materials. The structural properties of the substrates are shown to influence the electrical properties of the films.     

Dielectric properties of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped barium strontium calcium titanate thick films for microwave device applications

(Ba_0.56Sr_0.34Ca_0.10)TiO₃ (BSCT) thick films doped with 0.1 mol% MnCO₃ and Yb₂O₃ (0.1–0.7 mol%) were fabricated by the screen-printing method on the alumina substrate. The structural and electrical properties as a function of Yb₂O₃ amount were investigated. All BSCT thick films showed the formation of a complete solid solution in a cubic perovskite polycrystalline structure. Average grain size of the specimen doped with 0.7 mol% Yb₂O₃ was about 2.7 μm. The thickness of all BSCT thick films was approximately 50–55 μm. The relative dielectric constant, dielectric loss, and tunability of the BSCT thick films doped with 0.3 mol% Yb₂O₃ were 2,966, 0.7, and 14.3%, respectively.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

Investigation of Ba<Subscript>2-x</Subscript>Sr<Subscript>x</Subscript>TiO<Subscript>4</Subscript>: Structural aspects and dielectric properties

Investigation of solid solution of barium-strontium orthotitanates of the type, Ba_2-x Sr _x TiO₄ (0 ≤x≤ 2), show that pure phases exist only for the end members, Ba₂TiO₄ and Sr₂TiO₄, crystallizing in the β-K₂SO₄ and K₂NiF₄ structures, respectively. The intermediate compositions (till≥ 1) lead to a biphasic mixture of two Ba₂TiO₄-type phases (probably through a spinodal decomposition) with decreasing lattice parameters, indicating Sr-substitution in both the phases. Forx > 1, Sr₂TiO₄ along with a secondary phase is obtained. The dielectric constant and dielectric loss were found to decrease with Sr substitution till the nominal composition ofx = 1. However, pure Sr₂TiO₄ shows higher dielectric constant compared to the solid solution composition. Sr₂TiO₄ shows very high temperature stability of the dielectric constant.     

Characterization of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> prepared by low temperature chloride aqueous synthesis

Ba_0.9Sr_0.1TiO₃ powder was processed at 80°C by reacting Ti sol in aqueous solutions that contained BaCl₂, SrCl₂ and NaOH at atmospheric pressure. Well-crystallized, spherical, nanosizes powders were formed by this method. The powders were found to have a cubic structure, which was retained even after heating at 900°C. Sintering at 1400°C, led to the formation of a tetragonal structure with a secondary phase of Ba₆Ti₁₇O₄₀. Abrupt grain growth was observed at 1400°C. The electrical response of the sample sintered at 1400°C has three electrically different regions. Each region of the sample is represented by different RC element. Element 1 (R ₁ C ₁) is the most resistive and its capacitance ishigh (0.5 nFcm⁻¹) indicating a thin region, probably the grain boundary. Element 2 (R ₂ C ₂) shows a smaller resistance value compared to element 1. The capacitance value of element 2 is temperature-dependent and displays a Curie–Weiss behaviour, indicative of a ferroelectric material above T _c. The lower capacitance of C ₂ (15 pFcm⁻¹) indicates that it is a much thicker region than element 1 and can be assigned as a ferroelectric bulk region. Element 3 is probably an electrode effect.     

Structural,dielectric and impedance study of Bi and Li co-substituted Ba<Subscript>0.50</Subscript>Sr<Subscript>0.50</Subscript>TiO<Subscript>3</Subscript> ceramics for tunable microwave devices applications

In this article, the structural, dielectric and electrical properties of Bi and Li co-substituted (Ba, Sr) site in Ba_0.50Sr_0.50TiO₃ ceramics are presented. Four different compositions of Ba_0.50Sr_0.50TiO₃, (Ba_0.50Sr_0.50)_0.98(Bi, Li)_0.02TiO₃, (Ba_0.50Sr_0.50)_0.96(Bi, Li)_0.04TiO_3, and (Ba_0.50Sr_0.50)_0.92(Bi, Li)_0.08TiO₃ were synthesized using solid-state reaction with microwave heating of starting materials. Phase detection for all samples has been examined by XRD along with Rietveld refinement analyses, and the results show the formation of single phase without observation of any secondary phase. However, a decrease in crystallite size, lattice parameters, and unit cell volume has been observed with the increase of Bi and Li concentration. A Dense microstructure with different grains sizes and shapes has been obtained by scanning electron microscopy. Impedance spectroscopy in the temperature range of 30–300 °C and frequency range of 60 Hz–1 MHz has been used to study the dielectric properties. The result shows that the Bi and Li co-substituted Ba_0.5Sr_0.5TiO₃ ceramics exhibit very interesting features, such as enhanced dielectric constant with low loss which make it suitable for microwave tunable devices applications. An electric impedance analysis was carried out at different temperatures namely (400, 450, 500, and 550 °C). A single semicircular arc with single relaxation process has been observed in all studied samples which suggest that the grains contribute to the total resistance in these materials. The activation energy was obtained from the impedance analysis using Arrhenius plot of grain conductivity.     

Effects of solvent system on tape casting of the BaSrTiO<Subscript>3</Subscript>-MgO-based dielectric ceramics containing B<Subscript>2</Subscript>O<Subscript>3</Subscript>

Ba_0.6Sr_0.4TiO₃-MgO-based ceramic slurries with B₂O₃ and Li₂CO₃ as sintering aid were prepared with different solvent systems for tape casting application. The effects of azeotropic mixtures of toluene–ethanol, methyl ethyl ketone (MEK)–ethanol and zeotrpic mixture of xylene–ethanol with a mass ratio of 50:50 on Ba_0.6Sr_0.4TiO₃-MgO-based nonaqueous suspensions with B₂O₃ and Li₂CO₃ as sintering aid were investigated by sedimentation test, rheological measurement, density measurement, and SEM analysis. Without organic additives added, suspensions prepared with the MEK–ethanol mixture present higher flowability with lower viscosity, but less stability because of the smaller viscosity and density of MEK. On the other hand, with organic additives added, the gel structure is formed in slurries prepared with the toluene–ethanol mixture and xylene–ethanol mixture, caused by the reaction of the functional hydroxyl group of PVB and dissociated borate in the slurries. While slurries prepared with the MEK–ethanol mixture were more stable, exhibiting nearly Newtonian flow behavior and significantly lower viscosity.     

Dielectric properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Structural and dielectric properties of Bi doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ceramics

The dielectric properties of 0.1–15% mol bismuth doped Ba_0.6Sr_0.4TiO₃ (BST) ceramics have been investigated systematically. The solubility limit of bismuth is determined as about 10 mol% by means of both X-ray diffraction and scanning electron microscopy, which is further verified by the fact that the lattice constant of the samples above 10 mol% is almost invariable. The temperature dependence of the dielectric permittivity suggest that the ferroelectric behavior transit to relaxor ferroelectric type when impurity concentration reaches 5 mol%, and further to relaxor behavior for samples above 10 mol% Bi content, which is verified by the absence of a hysteresis loop. Thermal expansion results show differences between 5 and 10 mol% doped samples. Dielectric tunability at room temperature decreases with bismuth content increasing. The variation of properties was attributed to the impurity induced polar regions and former long-order structure.     

The effects of CuO-doping on dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Ba(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

CuO-doped lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT) and barium zirconate titanate (Ba(Zr_0.07Ti_0.93)O₃, BZT) were prepared via a multi-step solid-state reaction process. The BNT–BZT with CuO dopant ceramics sintered at 1150–1180 °C for 2 h in air showed a pure perovskite structure. SEM images reveal that a small amount of CuO (<2 mol%) play a significant role on the microstructure to improve its sintering attributes, while it will degrade when the dopant is added beyond 2 mol%. The dielectric and piezoelectric properties of CuO-doped BNT–BZT ceramics were evaluated. At room temperature, the sample doped with 2 mol% CuO shows quite good properties such as a high piezoelectric constant (d ₃₃ ∼156.5 pC/N) and a high electromechanical coupling factor (k _t ∼52%). The depolarization temperature increased dramatically and the maximum permittivity temperature decreased slightly.     

Effect of Ba Substitution for Sr in the Pb-based 1212 Cuprate Containing Sulfur of (Pb<Subscript>0.75</Subscript>S<Subscript>0.25</Subscript>)Sr<Subscript>2</Subscript>(Y,Ca)Cu<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">z</Emphasis></Subscript>

We already reported on the synthesis of new Pb-based 1212 layered cuprates containing sulfur in the (Pb_0.75S_0.25)Sr₂(Y,Ca)Cu₂O _z system. There none of the samples showed superconductivity until after annealing under high O₂ pressure. More recently, we have discovered that the samples could be substituted by Ba for Sr up to x=0.6 in the composition of (Pb_0.75S_0.25)(Sr_2−x Ba _x )(Y_0.4Ca_0.6) Cu₂O _z . Then if the Ba-substitution is performed for Sr, some of the almost-single phase samples are found to show resistivity drops and magnetic anomalies without annealing under high O₂ pressure. Among the samples, a sample with the nominal composition of (Pb_0.75S_0.25)(Sr_1.5Ba_0.5)(Y_0.4Ca_0.6) Cu₂O _z is found to show the highest onset temperatures of a resistivity drop at about 35 K and a magnetic anomaly at about 31.5 K. These are higher than the highest values for the superconducting Ba-free sample of (Pb_0.75S_0.25)Sr₂ (Y_0.4Ca_0.6)Cu₂O _z which was annealed under high O₂ pressure.     

Effect of annealing time on microstructure and morphology of thin films by sputtering deposition with (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> target

The ceramic thin films have been fabricated by radio frequency (RF) magnetron sputtering technique on SiO₂ (110) substrates with (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ target, and then the thin films were annealed at 1,150 °C for different times at O₂ atmosphere. The microstructure and morphology of the thin films were investigated as a function of the annealing times using the X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. The results show that the microstructure, morphology, and crystallinity of the thin films can be affected by the annealing times significantly. The main phases of the samples are indexed to be Ba_0.5Sr_0.5Nb₂O₆ and Ba_0.27Sr_0.75Nb₂O_5.78, which are different from component of the (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ target due to the volatilization of ZnO. The crystalline quality of the thin films decreases when the annealing time is shorter or longer than 30 min, and the roughness and grain size of the thin films reaches a maximum value when the annealing time is 30 min.     

Low-temperature magnetoresistance of biaxially strained 24-nm-thick La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films

The lateral unit cell parameter in nanodimensional La_0.67Ca_0.33MnO₃ (LCMO) films grown on (001)-oriented LaAlO₃ substrates is significantly (approximately 4%) smaller than the value measured along the normal to the substrate plane. At T < 140 K, the temperature dependence of the resistivity ρ of LCMO films follows the relation ρ − ρ (T = 4.2 K) ≈ρ₂(H)T ^4.5, where ρ₂ is independent of the temperature but decreases with increasing magnetic field H. It is shown that this decrease is related both to a decay of the spin waves in ferromagnetic domains and to the transformation of antiferromagnetic phase inclusions into ferromagnetic ones.     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.     

Low-temperature synthesis of Sr<Subscript>0.3</Subscript>Ba<Subscript>0.7</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> ultrafine powder and its characteristics

Ultrafine strontium barium niobate (Sr_0.3Ba_0.7Nb₂O₆, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO₃)₂, Ba (NO₃)₂, NbF₅, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature (1 kHz) was found to be 930 and below 0.025.     

Effect of the synthesis technique on the physicochemical properties of Ce<Subscript>0.8</Subscript>(Sm<Subscript>0.75</Subscript>Sr<Subscript>0.2</Subscript>Ba<Subscript>0.05</Subscript>)<Subscript>0.2</Subscript>O<Subscript>2 − δ</Subscript>

A multicomponent solid electrolyte of composition Ce_0.8(Sm_0.75Sr_0.2Ba_0.05)_0.2O_{2 − δ} has been synthesized by three different techniques: solid-state reaction, laser evaporation, and the glycine nitrate process. Its microstructure, sintering kinetics, and electrical properties have been studied in relation to the synthesis technique. Ceramics produced using laser evaporation consisted of submicron (0.2 μm) grains and offered the highest electrical conductivity: 27 × 10⁻³ S/cm at 873 K.     

Phase,microstructural characterization and dielectric properties of Ca-substituted Sr<Subscript>5</Subscript>Nb<Subscript>4</Subscript>TiO<Subscript>17</Subscript> ceramics

The effect of Ca substitution for Sr on the phase, microstructure and microwave dielectric properties of the Sr_5−x Ca _x Nb₄TiO₁₇ composition series was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), an LCR meter, and vector network analyzer. Below 1450 °C, Sr_5−x Ca _x Nb₄TiO₁₇ (x = 1, 2, 3, or 4) compositions formed single-phase Sr₄CaNb₄TiO₁₇, Sr₃Ca₂Nb₄TiO₁₇, Sr₂Ca₃Nb₄TiO₁₇, and SrCa₄Nb₄TiO₁₇ ceramics, respectively. At x = 0 and 5, Sr₅Nb₄TiO₁₇ and Ca₅Nb₄TiO₁₇ formed, but along with Sr₂Nb₂O₇ (at x = 0) and CaNbO₃ and CaNb₂O₆ (at x = 5) secondary phases. Above 1450 °C, all the compositions formed two-phase ceramics. At low frequencies, a phase transition was observed in the composition Sr₅Nb₄TiO₁₇. The substitution of Ca for Sr enabled processing of highly dense Sr₂Ca₃Nb₄TiO₁₇, with ε_r ~ 53.4, τ_f ~ −6.5 ppm/°C and Q _u  × f _o  ~ 1166 GHz. Further investigations are required to improve the quality factor of these ceramics for possible microwave applications.     

Optical anisotropy and dielectric parameters of (Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>)Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> films on a Pt(111)/Si(001) substrate

(Ba_0.5Sr_0.5)Nb₂O₆ films were synthesized on a Pt(111)/Si(001) substrate by RF gas-discharge sputtering in pure oxygen atmosphere. It was found that the films have a dominant crystallographic orientation in the [001] direction and natural unipolarity, which was revealed through analysis of dielectric and piezoelectric parameters. It was demonstrated that the optical parameters of film material in the Ba_0.5Sr_0.5, Nb₂O₆/Pt(111)/Si(001) heterostructure match those typical for a (Ba_0.5Sr_0.5)Nb₂O₆ single crystal.     

Effect of low level substitution of Sr–Ba on transport and magnetic behaviour of La<Subscript>0·67</Subscript>Ca<Subscript>0·33</Subscript>MnO<Subscript>3</Subscript>

In this paper we report the investigation of transition metal oxide compound, La_0·67Ca_0·25Sr_0·04Ba_0·04MnO₃ (LCSBMO), along with La_0·67Ca_0·33MnO₃ (LCMO), synthesized by sol–gel route under identical conditions. The effect of simultaneous low level substitution of large size ions such as Sr²⁺ and Ba^2 + for Ca^2 + ions on the electronic transport and magnetic susceptibility properties are analysed and compared apart from microstructure and lattice parameters. The temperature dependent electrical transport of the polycrystalline pellets of LCSBMO and LCMO when obeying the well studied law, r = r₀ + r₂   T²\rho = \rho_{0} + \rho_{2} \;T^{2} for T < T _MI , is observed to differ by more than 50% from the values of ρ ₀ and ρ ₂, with the former compound showing enhanced electrical conductivity than the latter. Similarly in fitting the adiabatic small polaron model for resistivity data of both the samples for T > T _MI , the polaron activation energy is found to differ by about 11%. In addition, the temperature dependent a.c. magnetic susceptibility study of the compounds shows a shift of about 6% in the paramagnetic to ferromagnetic transition temperature (285 K for LCSBMO and 270 K for LCMO).     

Low-temperature sintering and microwave dielectric properties of TiO<Subscript>2</Subscript>-based LTCC materials

Temperature stable high-K LTCC material was prepared. The influence of fabrication process on the crystalline phases, microstructures and microwave dielectric properties of TiO₂-Bi₂O₃-CuO ceramics were investigated. The crystalline phases and microstructures of TiO₂-Bi₂O₃-CuO ceramics were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. It was found that rutile TiO₂ phase and Bi₂Ti₄O₁₁ phase co-existed in the TiO₂-Bi₂O₃-CuO ceramics. Separate TiO₂ grains and Bi₂Ti₄O₁₁ grains distributed uniformly in the ceramic matrix. The composition 0.92TiO₂-0.08Bi₂Ti₄O₁₁ with 2 wt% CuO addition that was sintered at 900 °C for 2 h showed high dielectric constant (ε_r ~ 81), high quality factor (Q × f ~ 3,500 GHz) and near zero temperature coefficient of resonant frequency (τ_f ~ −5.1 ppm/°C), meanwhile the compatibility test showed that it could co-fire with silver electrode. The processing-microstructure-property interrelationship was also studied.