Microstructure and secondary phases in epitaxial LaBaCo_2O_(5.5 + δ) thin films

Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo_2O_(5.5 + δ)(LBCO) thin films grown on SrTiO_3(STO) substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]_(LBCO)//[100]_(STO)and(001)_(LBCO)//(001)_(STO). Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 90℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001]direction of the film. In the film grown at a temperature of 1000℃, isolated nano-scale Co_3O_4 particles appeared, which promoted the growth of {111} twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.     

Effect of substrate on microstructure and mechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Lead-free ferroelectric (K, Na)NbO₃ (KNN) thin films (～200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al₂O₃ and Pt/SiO₂/Si substrates and sintered at 650 °C. Pure perovskite phase of K_0.65Na_0.35NbO₃ in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na₂Nb₈O₂₁ phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (～7.4 nm) and contained spherical (～50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.     

Effect of tetragonal perovskite phase addition on the electrical properties of KNN thick films fabricated by aerosol deposition

The effect of complex-perovskite-materials (CPs) doping on phase transition and dielectric/ferroelectric properties was investigated in lead-free 0.985[0.92(Na_0.535K_0.48)NbO₃–0.08LiNbO₃]–0.015CPs (KNN–Li–CPs) films. Three CPs were selected: Ba(Cu_1/3Nb_2/3)O₃ (BCN), Ca(Cu_1/3Nb_2/3)O₃ (CCN), and Sr(Cu_1/3Nb_2/3)O₃ (SCN). The films were fabricated by aerosol deposition (AD) method. In the KNN–Li–BCN film annealed at 700 °C for 1 h in air, the ferroelectric and dielectric properties (75% P_r at 400 kV/cm and 40% ε_r) were increased compared to those of the KNN-Li film, which was attributed to the variation of phase, secondary phases, and the softening effect of the dopants.     

Tailoring the domain structure of epitaxial BiFeO3 thin films

Control of the ferroelastic and ferroelectric domain structure of BiFeO₃ through the use of epitaxial growth on substrates with reduced symmetry is reviewed. The first approach presented utilizes orthoscandate substrates, specifically TbScO₃, to reduce the number of possible ferroelastic domains from 4 to 2. Experimental results and phase field simulations are presented which are in agreement with the theory of anisotropic strain relaxation, due to differing in-plane lattice parameters of the orthorhombic substrate, causing a reduction in the possible domains. The second approach that is presented involves the use of miscut cubic substrates, such as SrTiO₃, to tailor the domain structure from 4-domain to 2- or single-domain is presented, the former being achieved with a miscut in the [1 0 0] direction and the latter with a miscut in the [1 1 0] direction, assuming a film normal orientation of [0 0 1]. The use of these techniques in understanding the fundamental nature of the ferroelastic and ferroelectric properties in BiFeO₃, and the use of these methods in tailoring BiFeO₃ to meet the needs of future device applications is discussed.     

Stacking faults in an epitaxially grown PbTiO3 thick film and their size distribution

The microstructure of an epitaxial PbTiO₃ thick film, grown on a SrRuO₃/SrTiO₃ substrate at 600 °C by pulsed-MOCVD method, was investigated by using transmission electron microscopy. A number of extrinsic or intrinsic stacking faults were observed in the epitaxial PbTiO₃ thick film and they were parallel to the (0 0 1) plane of the PbTiO₃. We also investigated the size distribution of these stacking faults. The width of these stacking faults along the [1 0 0] axis of the PbTiO₃ was very small, ranging from 2 to 13 nm. It was also revealed that the size distribution of stacking faults depends on the position in the film: near the surface, near the substrate, near threading dislocations, and near 90° domain boundaries.     

New dielectric materials of xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 ceramic system at microwave frequency

The crystal structures and the microwave dielectric properties of the xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ perovskite ceramic system have been investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. SrTiO₃ has dielectric properties of dielectric constant ε_r ∼ 205, Q × f value ∼ 4200 GHz and a large positive τ_f value ∼ 1700 ppm/°C. Ca(Mg_1/3Nb_2/3)O₃ possesses high dielectric constant (ε_r ∼ 28), high quality factor (Q × f value ∼ 58,000 at 7 GHz) and negative τ_f value (− 48 ppm/°C). As the x value varies from 0.2 to 0.8, the xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ system has the dielectric properties as follows: 40 < ε_r < 123, 4600 < Q × f < 33,400 and − 23 < τ_f < 600. A new microwave dielectric material, 0.3SrTiO₃–0.7Ca(Mg_1/3Nb_2/3)O₃, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ε_r ∼ 46, a Q × f value ∼ 29,300 GHz (at 6.8 GHz) and a τ_f value ∼− 2 ppm/°C. A near-zero τ_f value can be achieved by adjusting the x value of xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ ceramics.     

Surface evolution and dynamic scaling of heteroepitaxial growth of (La,Ba)MnO3 films on SrTiO3 substrates by rf magnetron sputtering

We have investigated the evolution of (La_0.7Ba_0.3)MnO₃ (LBMO) surfaces epitaxially grown on SrTiO₃ (001) substrates using high-resolution X-ray scattering and atomic force microscopy (AFM) measurements. At an early stage of growth, highly strained LBMO epilayers were formed and nearly pseudomorphic growth of LBMO epilayers on SrTiO₃ substrates was expected. For these thin layers, roughness varied with thickness through a scaling exponent β = 0.102 ± 0.01. As the LBMO epilayer thickness attained 72 nm, the growth front of the film became quite rough, which is related to the relief of strain. From AFM images, distinct large 3-D islands were formed on the rough film surface in the regime of rapid roughening; this regime is described with a scaling exponent β = 0.734 ± 0.01. An effective critical thickness of a LBMO film epitaxially grown on a SrTiO₃ substrate is experimentally determined to be about 50–72 nm.     

Rapid synthesis of pervoskites (KNbO3, SrTiO3) and spinel (LiMn2O4) in presence of α-glycine with finished end product

Addition of Amino acid α-glycine to pervoskites like potassium niobate (KNbO₃) and strontium titanate (SrTiO₃) is seen to reduce the temperature of synthesis by several 100 degrees leading to formation of fine end product. Reduction of the grain size as much as 27% has been recorded in KNbO₃. The XRD Intensities were found to depend on the molar proportion of glycine. The average particle size of the KNbO₃ product with glycine is found to be in order of 140–290 nm having maximum tetragonal distortion of 1.206. SrTiO₃ synthesised in presence of glycine shows needle shaped structures with reduction in white aggregates. Glycine helps in liberation of carbon dioxide with fishy odour thereby leading to the early phase formation. Studies on LiMn₂O₄ spinel used in rechargeable lithium batteries in this direction have been included.     

Heteroepitaxial growth of δ-Bi2O3 thin films on CaF2(1 1 1) by chemical vapour deposition under atmospheric pressure

We have succeeded in achieving the heteroepitaxial growth of a δ-Bi₂O₃ thin film on a CaF₂(1 1 1) substrate by means of chemical vapour deposition under atmospheric pressure. The film grew with a strong (1 1 1) orientation. From X-ray pole figures, it was observed that the δ-Bi₂O₃ film grew on the CaF₂(1 1 1) substrate with 60° rotational in-plane domains. The growth mode was of a 3D island type, and the grain size decreased with increasing oxygen pressure during the δ-Bi₂O₃ film growth, improving the overall surface smoothness.     

Epitaxial La2 / 3Sr1 / 3MnO3 thin films with unconventional magnetic and electric properties near the Curie temperature

We used Pulsed Laser Deposition (PLD) in oxidizing environment to epitaxially grow optimally doped manganite La_2 / 3Sr_1 / 3MnO₃ (LSMO) thin films over a (001) oriented SrTiO₃ substrate. Synthesized samples show good room temperature magnetic properties accompanied by a peculiar extension of the metallic conduction regime to temperatures higher than the Curie point.In this paper we present a study of the dependence of transport and magnetic properties of LSMO thin films on the oxygen pressure during PLD growth. We show how interaction of the growing films with O₂ molecules is fundamental for a correct synthesis and in which way it is possible to adjust PLD experimental parameters in order to tune LSMO thin film properties.The persistence of the metallic conduction regime above the Curie temperature indicates some minor changes of the electronic structure near the Fermi level, which is responsible for the half-metallic behavior of LSMO at low temperature. This feature is rather intriguing from the technological point of view, as it could pave the way to the increase of operating temperature of devices based on LSMO.     

The effect of B-site cations on the properties of KTaxNb1−xO3 [1 0 0] surface: A study of density functional theory

Ferroelectric material and piezoelectric properties are different in potassium tantalite niobate (KTa_xNb_1−xO₃) crystal according to differences in x. Here, we show the results of KTa_xNb_1−xO₃ (x = 0.25, 0.5, 0.75) crystal [1 0 0] surface properties calculated by density functional theory (DFT). Using local density approximation (LDA) and generalized gradient approximation (GGA), DFT has been employed to determine the structural, electronic, and optical properties of chemically ordered ferroelectric KTa_xNb_1−xO₃ crystal [1 0 0] surfaces. Based on the research, comparison and analysis of the results show that all kinds of properties of KTa_xNb_1−xO₃ [1 0 0] surfaces are vary with respect to x. It is found, for instance, that the ordering of B-site cations obviously influences the properties of the KTa_xNb_1−xO₃ surface. At the same time, this allows the experimental studies to be supervised effectively.     

Synthesis of TiO2 thin films using single molecular precursors by MOCVD method for dye-sensitized solar cells application and study on film growth mechanism

For dye-sensitized solar cells application, in this study, we have synthesized TiO₂ thin films at deposition temperature in the range of 300–750 °C by metalorganic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, {TIP, Ti(OⁱPr)₄} and Bis(dimethylamido)titanium diisopropoxide, {BTDIP, (Me₂N)₂Ti(OⁱPr)₂} were used as single source precursors that contain Ti and O atoms in the same molecule, respectively. Crack-free, highly oriented TiO₂ polycrystalline thin films with anatase phase were deposited on Si(1 0 0) with TIP at temperature as low as 450 °C. XRD and TED data showed that below 500 °C, the TiO₂ thin films were dominantly grown in the [2 1 1] direction on Si(1 0 0), whereas with increasing the deposition temperature to 700 °C, the main film growth direction was changed to [2 0 0]. Above 700 °C, however, rutile phase TiO₂ thin films have only been obtained. In the case of BTDIP, on the other hand, only amorphous film was grown on Si(1 0 0) below 450 °C while a highly oriented anatase TiO₂ film in the [2 0 0] direction was obtained at 500 °C. With further increasing deposition temperatures over 600 °C, the main film growth direction shows a sequential change from rutile [1 0 1] to rutile [4 0 0], indicating a possibility of getting single crystalline TiO₂ film with rutile phase. This means that the precursor together with deposition temperature can be one of important parameters to influence film growth direction, crystallinity as well as crystal structure. To investigate the CVD mechanism of both precursors in detail, temperature dependence of growth rate was also carried out, and we then obtained different activation energy of deposition to be 77.9 and 55.4 kJ/mol for TIP and BTDIP, respectively. Also, we are tested some TiO₂ film synthesized with BTDIP precursor to apply dye-sensitized solar cell.     

In–Ga–Zn–O thin film transistor with HfO2 gate insulator prepared using various O2/(Ar + O2) gas ratios

We have investigated the effect of the deposition of an HfO₂ thin film as a gate insulator with different O₂/(Ar + O₂) gas ratios using RF magnetron sputtering. The HfO₂ thin film affected the device performance of amorphous indium–gallium–zinc oxide transistors. The performance of the fabricated transistors improved monotonously with increasing O₂/(Ar + O₂) gas ratio: at a ratio of 0.35, the field effect mobility of the amorphous InGaZnO thin film transistors was improved to 7.54 cm²/(V s). Compared to those prepared with an O₂/(Ar + O₂) gas ratio of 0.05, the field effect mobility of the amorphous InGaZnO thin film transistors was increased to 1.64 cm²/(V s) at a ratio of 0.35. This enhancement in the field effect mobility was attributed to the reduction of the root mean square roughness of the gate insulator layer, which might result from the trap states and surface scattering of the gate insulator layer at the lower O₂/(Ar + O₂) gas ratio.     

Preparation and characterization of quenched KNbO3-Nb2O5 glass

KNbO₃-Nb₂O₅ glasses were prepared with molar ratio of K/(K + Nb) from 0.16 to 0.5 by using a twin-roller quenching apparatus. Most KNbO₃-Nb₂O₅ glasses crystallized to stable phases such as KNbO₃, K₂Nb₄O₁₁, K₃Nb₇O₁₉, KNb₃O₈ and K₂Nb₈O₂₁ via metastable phases after heat treatment and K₄Nb₆O₁₇ glass directly crystallized to K₄Nb₆O₁₇ crystal. KNbO₃ glass consisted of the corner-shared NbO₆ octahedra, while the amounts of the edge-shared NbO₆ octahedra in the KNbO₃-Nb₂O₅ glass structure increased with decreasing K⁺ ion content. The band gap energies and the ionic conductivity of the KNbO₃-Nb₂O₅ glasses increased with increasing K⁺ ion content, but the density and the activation energy of the ionic conduction decreased. The glasses possessed high dielectric constants appfoaching those of ferroelectric crystals at high temperature around the crystallization temperature. The dielectric constants of the glasses, however decreased greatly with decreasing temperature and with increasing frequency.     

Electromechanical properties of [0 0 1], [0 1 1] and [1 1 1] oriented Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 crystals under uniaxial stress

The electric field and the stress induced strain and polarization responses of [0 0 1], [0 1 1] and [1 1 1] oriented Pb(Mg_1/3Nb_2/3)O₃–0.32PbTiO₃ (PMN–0.32PT) relaxor ferroelectric single crystals have been systematically investigated by experimental study. The responses of [0 0 1] oriented single crystal to stress cycle and electric field are explained by polarization rotation and phase transformations mechanism. However, the responses of [0 1 1] and [1 1 1] oriented single crystal should be explained by domain switching. The differences of strain and polarization between the minimum and maximal values of electric field in [0 0 1] orientation firstly increase then decrease with enhancing of compressive stress.     

Properties of highly oriented K(Sr,Ba)2Nb5O15 thin films derived from a metal-alkoxide precursor solution

Highly oriented tungsten–bronze K(Sr,Ba)₂Nb₅O₁₅ (KSBN) thin films have been fabricated by a chemical solution deposition method. Alkoxy-derived K(Sr_0.5Ba_0.5)₂Nb₅O₁₅ (KSBN50) thin films directly crystallized into a tetragonal tungsten–bronze phase on fused silica, MgO(1 0 0), and Pt(1 0 0)/MgO(1 0 0) substrates with c-axis preferred orientation at 700 °C by optimizing the processing conditions. Ferroelectric KSBN50 thin films on Pt(1 0 0)/MgO(1 0 0) exhibited the diffuse-phase transition and typical relaxor-type dielectric behavior, which are characteristic properties along the c-axis of the tungsten–bronze (Sr,Ba)Nb₂O₆ crystal. The KSBN thin films synthesized on fused silica and MgO(1 0 0) showed high transparency over a wide wavelength range. The propagation modes of the synthesized KSBN thin films were characterized by the prism coupling method. The values of their refractive indices in TE and TM modes were 2.27 and 2.25, respectively.     

The strain reduction and quality improvement in ZnO film by a 30° in-plane rotation with respect to the Al2O3 substrate

The in-plane orientation of epitaxial ZnO thin film on Al₂O₃(0 0 0 1) was determined by azimuthal scan of X-ray diffraction. Comprehensive structural characterizations, including the lattice strain in perpendicular direction, the defect density, were obtained from high resolution X-ray diffraction. It's found that a 30° rotation in ZnO against Al₂O₃, resulting in ZnO〈1 1 2 0〉//Al₂O₃〈1 0 1 0〉, can efficiently reduce the strain and defects in ZnO layer. Consequently, the optical property is significantly improved.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Application of carbonated apatite coating on a Ti substrate by aqueous spray method

The fabrication and characterization of a carbonate-containing apatite film deposited on a Ti plate via an aqueous spray method is described. The mist of the spray solution emitted from a perpendicularly oriented airbrush was made to strike a warmed Ti substrate. The thicknesses of the sprayed film and those heat-treated at 400 °C–700 °C under Ar gas flow were in the range 1.21–1.40 μm. The results of elemental analyses and Fourier transform infrared spectroscopy of the powders that were mechanically collected from the surface of the sprayed film suggest that the film was Ca₁₀(PO₄)6(CO₃) · 2CO₂ · 3H₂O. The presence of the carbonate ion and the lattice CO₂ molecule was confirmed via the aforementioned analyses; the finding was also consistent with the X-ray diffraction patterns of the films and the chemical identity of the sprayed and heat-treated films that were measured using X-ray photoelectron spectroscopy. The sprayed film comprises a characteristic network structure, which contains round particles within the networks, as was observed by field-emission scanning electron microscopy. A scratch test indicated that the shear stress of the sprayed film (21 MPa) significantly improved to 40 and > 133 MPa after heat-treatment at 600 °C and 700 °C, respectively, under Ar gas flow for 10 min.     

Electrochemical performance of Y2O3/NiO cathode in the molten Li0.62/K0.38 carbonates eutectics

The preparation and subsequent oxidation of Ni cathodes modified by impregnation with yttria were evaluated by surface and bulk analysis. The electrochemical behavior of Y₂O₃/NiO cathodes was also evaluated in a molten 62 mol% Li₂CO₃ + 38 mol% K₂CO₃ eutectic at 650 °C by electrochemical impedance spectroscopy (EIS) as a function of yttria content and immersion time under the standard cathode gas condition (CO₂:O₂ = 67:33%). The stability tests of Y₂O₃/NiO cathodes showed that the yttria additive could dramatically reduce the solubility of NiO in the eutectic molten Li/K carbonates due to the preferential dissolution of yttria. The loss of yttria was confirmed by chemical analysis and X-ray diffraction (XRD). The Y₂O₃/NiO cathodes showed higher catalytic activity for oxygen reduction and lower dissolution of NiO than the pure NiO cathode. The cathode material with 1.0 wt.% of yttria showed the optimum behavior.