Determination of the atomic structure of a Σ13 SrTiO<Subscript>3</Subscript> grain boundary

New elements of a symmetric [001] 67.4^∘ SrTiO₃ near Σ 13 tilt grain boundary are identified by a quantitative analysis of lattice images, reconstructed electron exit waves, and HAADF images. The analysis reveals local, geometrical variations of structural grain boundary units that relate to the presence of defects introduced by a tilt deviation of 0.65 + 0.02 degrees from the perfect Σ13 geometry. Sr and TiO columns are discriminated in HAADF images while the reconstructed electron exit wave reveals all oxygen columns in addition. Both methods depict the crystal and boundary structure directly while lattice imaging with a high voltage instrument requires image simulations to link the image intensity to structure. For the first time we observe a Sr column splitting by 90 pm that supports theoretical predictions. An inhomogeneous, preferential etching at the grain boundary is attributed to local charge variations and hampers a quantitative investigation and local stoichiometry. The near Σ13 boundary forms a dense and compact structure with chemically identical columns in close proximity. Therefore, it is different from the relaxed, bulk like configurations described in previous reports.     

The Electrocaloric Effect in BaTiO<Subscript>3</Subscript>–SrTiO<Subscript>3</Subscript> Solid Solution

We have studied the electrocaloric effect in 0.68BaTiO₃–0.32SrTiO₃ solid solution, as well as the dielectric, pyroelectric, and piezoelectric properties of this compound in the vicinity of the first-order phase transition in a bias electric field. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.     

Preparation of SrTiO<Subscript>3</Subscript> nanomaterial by a sol–gel-hydrothermal method

A new synthetic route to obtain high-purity strontium titanate, SrTiO₃, using the sol–gel-hydrothermal reaction of TiCl₄ and a SrCl₂ solution in an oxygen atmosphere has been developed. In the synthesized products the SrTiO₃ nanoparticles are nearly spherical and decrease in size with the reaction time (48 h) down to a diameter of about 40 nm. The microstructure and composition of the as-synthesized samples were investigated by X-ray diffraction (XRD), high-resolution TEM (HRTEM), Raman spectroscopy, atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDX). All the samples were identified as cubic perovskite phase.     

Investigation on the Current Transport Characteristics of SrTiO<Subscript>3</Subscript>/YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−x</Subscript> Heterostructure

By the combined use of the sol-gel and pulsed laser deposition methods, the SrTiO₃/YBa₂Cu₃O_7?x (STO/YBCO) heterostructure was prepared on a LaAlO₃ substrate. XRD results and φ scanning test showed that the prepared STO/YBCO heterostructure had good biaxial texture. Moreover, a Pt electrode was sputtered on the STO/YBCO heterostructure to investigate the current density-voltage (J ? V) characteristic curves of STO/YBCO in the 50–300 K temperature range. The results showed that the STO/YBCO heterostructure had good rectifying characteristics. With an applied positive bias voltage smaller than 3.7 V, the current density of the STO/YBCO heterostructure decreased with the decrease of temperature; for higher voltages, on the contrary, the current density increased with the decrease of temperature. When the YBCO experienced superconducting transition, the turn-on voltage (V _t) changed suddenly due to the sudden opening of the superconducting energy gap of YBCO. The V _t variation obtained from the experiment was essentially consistent with the known value of the YBCO superconducting energy gap.     

Enhanced dielectric and piezoelectric properties of (100) oriented Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–SrTiO<Subscript>3</Subscript> thin films

The (100) oriented and random oriented 0.755Bi_0.5Na_0.5TiO₃–0.065BaTiO₃–0.18SrTiO₃ (BNT–BT–ST) thin films were deposited on LaNiO₃ (LNO) buffered Pt(111)/Ti/SiO₂/Si substrates by the sol–gel processing technique. The orientation is controlled by the concentration of solution. The structure, dielectric and piezoelectric properties of the thin films are significantly affected by the crystallographic orientation. The (100) oriented BNT–BT–ST thin film has improved dielectric and piezoelectric properties. For the (100) oriented and random oriented BNT–BT–ST thin films, the dielectric constants are 660 and 550, the dielectric losses are 0.045 and 0.076 and the effective piezoelectric coefficients are 140 and 110 pm/V, respectively. The large piezoelectric response is attributed to the uniform microstructure and increased lattice distortion along (100) direction.     

HRXRD Analysis for YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> Deposited on {001} SrTiO<Subscript>3</Subscript>

YBa₂Cu₃O_7−x (YBCO) film was deposited on {001} SrTiO₃ (STO) substrate by pulse laser deposition (PLD). The microstructure of YBCO and STO was analyzed by High resolution X-ray diffraction (HRXRD). The results showed that the YBCO film alignment was C-axis coexisting with about 1 vol.% a-axis, and the spreading of YBCO’s out-plane alignment is anisotropic inherited from STO’s. In addition, there was 90° 〈110〉 twin domain with in-plane distort angle ±0.85° distort angle in the film, which was caused by T-O phase transition.     

The role of vicinal Σ3 boundaries and Σ9 boundaries in grain boundary engineering

Σ 3 grain boundary planes and triple junctions containing Σ 3 boundaries have been investigated in grain boundary engineered brass using an adaptation of electron backscatter diffraction (EBSD) data combined with a single surface trace analysis methodology. The data have been analysed from the standpoint of whether or not the interface planes in the Σ 3 boundaries are close to {111} (i.e. coherent annealing twins), vicinal to {111} (i.e. a small deviation from the {111} reference structure) or not on {111}. At triple junctions composed of Σ 3/Σ 3/Σ 9 it was shown that a combination of one {111} and one vicinal-to-{111} Σ 3 was more likely to occur than two {111} Σ 3s or two not-{111} Σ 3s. The explanation for the preferred {111}/vicinal-to-{111} combination is that mobile Σ 9 boundaries with high deviations encounter {111} Σ 3s, and in consequence regenerate a Σ 3 at the triple junction which must be vicinal-to-{111} according to the crystallographic constraints at the junction. Analysis of the not-{111} Σ 3s indicated that more than half the boundaries in this category could not have {211}{211}, {774}{855}, {111}{511}, {001}{221} or {110}{411} planes. The possible distribution of these planes types, based on information from the single-surface trace analysis, had a high rank correlation coefficient, 0.925, with previous data from nickel which was based on a two-surface, full boundary planes analysis.     

Molten-salt synthesis of Cu–SrTiO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanotube heterostructures for photocatalytic water splitting

A series of Cu-loaded SrTiO₃/TiO₂ nanotube heterostructures were synthesized by a facile molten salts method and an impregnation-calcination method. Through adjusting the molar ratio of Sr/Ti, the photocatalytic performance of the samples changed regularly. When Sr/Ti = 0.2, the catalyst showed the highest performance in water splitting and the H₂ generation amount was 0.597 mmol under UV irradiation for 8 h. The enhanced performance of Cu-loaded SrTiO₃/TiO₂ nanotubes could be attributed to the heterostructures, the small crystallite size, and the reduced band gap inside them.     

Microstructure and microwave properties of {CaT{i}O}<Subscript>3</Subscript>–LaGaO<Subscript>3</Subscript> {solid solutions}

The phase assemblage, microstructure and microwave (MW) properties of xCaTiO₃-(1-x)LaGaO₃ (CT-LG) ceramics prepared by solid state synthesis from raw oxides and carbonates have been investigated. LG was predominantly single phase perovskite with space group, Pnma, but a small quantity of pyrochlore structured La₂Zr₂O₇ second phase was present due to the contamination from the ZrO₂ milling media. At MW frequencies, the temperature coefficient of resonant frequency (τ_{f}) of LG was --80~ppm/\({\circ}\)C, its permittivity, \(\varepsilon_{r} {=} \)27 and MW quality factor, \(Q^{*}f_{o} {=} \)97,000 (@5~GHz). As CT concentration increased, \(\tau_{f}\) and \(\varepsilon_{r}\) increased to The phase assemblage, microstructure and microwave (MW) properties of xCaTiO₃-(1-x)LaGaO₃ (CT-LG) ceramics prepared by solid state synthesis from raw oxides and carbonates have been investigated. LG was predominantly single phase perovskite with space group, Pnma, but a small quantity of pyrochlore structured La₂Zr₂O₇ second phase was present due to the contamination from the ZrO₂ milling media. At MW frequencies, the temperature coefficient of resonant frequency (τ_{f}) of LG was --80~ppm/ C, its permittivity, 27 and MW quality factor, 97,000 (@5~GHz). As CT concentration increased, and increased to $+$850~ppm/ C and 160, respectively but decreased to 20,000. Zero was achieved at 0.65 with 47, and 40,000, properties comparable with commercial compositions. However, for 0.5, a different second phase was observed which was rich in Ca and Ga. Electron diffraction patterns could be indexed according to a body centred cubic lattice, 12.5 ?. It is suggested that the presence of second phases in the CT-LG compounds may, in part, be responsible for the deterioration in .     

Increased mobility of an <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> grain boundary by electron-beam irradiation

When subjected to electron-beam irradiation in a transmission electron microscope, the grain boundary in an α-Al₂O₃ bicrystal is observed to migrate even at room temperature. The bicrystal is composed of grains with the same normal direction, and thus the difference in strain energy or surface energy between the two grains cannot explain the observed migration. We attribute this phenomenon to an increase in grain boundary mobility by electron-beam irradiation, especially by radiolysis effects.     

Thermoelectric properties of transition metals-doped Ca<Subscript>3</Subscript>Co<Subscript>3.8</Subscript>M<Subscript>0.2</Subscript>O<Subscript>9+δ</Subscript> (M = Co,Cr, Fe,Ni, Cu and Zn)

The thermoelectric properties of the Ca₃Co₄O_9+δ and the transition metals-doped Ca₃Co_3.8M_0.2O_9+δ (where M = Cr, Fe, Ni, Cu and Zn) ceramics were reported. Ca₃Co₄O_9+δ single phase was checked by using X-ray diffraction analysis performed for the Ca₃Co_3.8M_0.2O_9+δ samples. The scanning electron micrographs showed some degrees of grains alignment in the compacted direction. The resistivity of the samples measured from 100 up to 700 °C varies in magnitude for different transition metals substitution. The variation of resistivity was explained by a change of carrier concentration induced by the doped ions. The thermopower increased with increasing temperature but showed no obvious change for any transition metals doping. The thermal conductivities changed for the doped samples but were relatively independent of temperature. The ZT was calculated to be the highest for the Fe substitution for the whole measurement temperature with the maximum value of 0.12 at 700 °C.     

Preparation and sintering behaviour of a fine grain BaTiO<Subscript>3</Subscript> powder containing 10 mol% BaGeO<Subscript>3</Subscript>

The formation of solid solutions of the type [Ba(HOC₂H₄OH)₄][Ti_1−x Ge _x (OC₂H₄O)₃] as Ba(Ti_1−x /Ge _x )O₃ precursors and the phase evolution during thermal decomposition of [Ba(HOC₂H₄OH)₄][Ti_0.9Ge_0.1(OC₂H₄O)₃] (1) are described herein. The 1,2-ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO₃ and BaGeO₃. A heating rate controlled calcination procedure, up to 730 °C, leads to a nm-sized Ba(Ti_0.9/Ge_0.1)O₃ powder (1a) with a specific surface area of S = 16.9 m²/g, whereas a constant heating rate calcination at 1,000 °C for 2 h yields a powder (1b) of S = 3.0 m²/g. The shrinkage and sintering behaviour of the resulting Ba(Ti_0.9/Ge_0.1)O₃ powder compacts in comparison with nm-sized BaTiO₃ powder compacts (2a) has been investigated. A two-step sintering procedure of nm-sized Ba(Ti_0.9/Ge_0.1)O₃ compacts (1a) leads, below 900 °C, to ceramic bodies with a relative density of ≥90%. Furthermore, the cubic ⇆ tetragonal phase transition temperature has been detected by dilatometry, and the temperature dependence of the dielectric constant (relative permittivity) has also been measured.     

Microwave and photoluminesent characterizations of (Ca<Subscript>2</Subscript>Mg<Subscript>3</Subscript>)(X<Subscript>1.75</Subscript>Sb<Subscript>0.25</Subscript>)TiO<Subscript>12</Subscript> [X = Nb and Ta] ceramics

(Ca₂Mg₃)(X_1.75Sb_0.25)TiO₁₂ [X = Nb and Ta] ceramics are prepared through the conventional solid-state route. The samples are calcined at 1,100 and 1,180 °C, and are sintered at 1,250 and 1,375 °C. The substitution of Sb decreases the calcination and sintering temperatures of pure (Ca₂Mg₃)(Nb/Ta)₂TiO₁₂. The structure of the samples is analyzed using X-ray diffraction method. The microstructure of the sintered pellet is studied using scanning electron microscopy. The dielectric properties such as dielectric constant (ε_r), quality factor (Q_uxf) and temperature coefficient of resonant frequency (τ_f) are measured in the microwave frequency region. By Sb substitution, thermal stability is achieved, with the increase in dielectric constant, without much change in the quality factor. The materials have intense emission lines in the wavelength region 500–700 nm. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Enhanced electrical characteristics of sol–gel-derived amorphous SrTiO<Subscript>3</Subscript> films

Amorphous SrTiO₃ thin films were fabricated on Pt (100)/Ti/SiO₂/Si substrates by sol–gel and spin-coating technology and their surface and cross-section morphology were characterized by using field emission scanning electron microscopy. A broad absorption band at about 3390 cm^?1 owing to the stretching vibrations of hydroxyl groups in the absorbed water was observed from fourier transform infrared spectroscopy. J–E measurements were used to investigate the electrical characteristics of SrTiO₃ films. The breakdown characteristics and leakage current are strongly dependent upon their electrode materials. SrTiO₃ films with Al top electrodes exhibit significantly higher breakdown strength and much lower leakage current than those with Au top electrodes. Moreover, samples with Al electrodes exhibit distinct electrical characteristics when a negative voltage was applied under different testing conditions. The surface chemical state of aluminum was analyzed by using X-ray photoelectron spectroscopy, indicating that the 45 nm thick Al electrode was completely transformed into aluminum oxide layer when a positive voltage was applied. These results show that the anodic oxidation of the Al electrodes and films is suggested to be responsible for the enhanced electrical characteristics of SrTiO₃ thin films.     

Phase equilibria in the Tl<Subscript>5</Subscript>Te<Subscript>3</Subscript>–Tl<Subscript>9</Subscript>BiTe<Subscript>6</Subscript>–Tl<Subscript>9</Subscript>TbTe<Subscript>6</Subscript> system

Phase equilibria in the Tl₅Te₃–Tl₉BiTe₆–Tl₉TbTe₆ system have been studied using differential thermal analysis, X-ray diffraction, and microhardness measurements. We have mapped out a number of vertical sections, the 760-K isothermal section of its phase diagram, and projections of its liquidus and solidus surfaces. The composition dependences of lattice parameters and microhardness have been obtained. The system has been shown to contain a continuous series of solid solutions, which crystallize in a tetragonal structure (Tl₅Te₃ type, sp. gr. I4/mcm).     

A Comparative Study of Angle Dependent Magnetoresistance in [001] and [110] La<Subscript>2/3</Subscript>Sr<Subscript>1/3</Subscript>MnO<Subscript>3</Subscript>

The angle dependent magnetoresistance study on [001] and [110] La_2/3Sr_1/3MnO₃ thin films shows that the anisotropy energy of [110] films is higher than that of a [001] oriented La_2/3Sr_1/3MnO₃ film of similar thickness. The data have been analyzed in the light of a multidomain model and it is seen that this model correctly explains the observed behavior.     

Preparation,characterization and dielectric properties of Ba<Subscript>3−x</Subscript>Sr<Subscript>x</Subscript>LiM<Subscript>3</Subscript>Ti<Subscript>5</Subscript>O<Subscript>21</Subscript>[M=Nb and Ta,x = 0 to 3] ceramics

The ceramic compositions Ba_3−xSr_xLiM₃Ti₅O₂₁[M=Nb and Ta, x = 0 to 3] were prepared through conventional solid state ceramic route. A detailed study has been carried out to correlate the structure of Ba_3−xSr_xLiM₃Ti₅O₂₁[M=Nb and Ta, x = 0 to 3] with respect to their dielectric properties. The structure and microstructure of ceramic samples were studied using powder X-ray diffractometer and Scanning Electron Microscopic techniques. The dielectric properties of the sintered ceramic compacts have been studied. The Ba-rich compositions were identified as promising candidates for high frequency applications whereas the Sr-rich compositions were excellent ionic conductors and can be commercially exploited for applications in solid-state batteries.     

Microwave dielectric properties of novel rare earth based silicates: RE<Subscript>2</Subscript>Ti<Subscript>2</Subscript>SiO<Subscript>9</Subscript> [RE = La,Pr and Nd]

The RE₂Ti₂SiO₉ [RE = La, Nd and Pr] ceramics are synthesized by solid state ceramic route. These materials exhibit a relative permittivity of about 30 with quality factor in the range 19,600–33,700 GHz. They also showed relatively low values of τ_f. The microwave dielectric properties of these materials are studied for the first time. The La_2−xPr_xTi₂SiO₉ [x = 0–2] based solid solution are also synthesized and single phase is confirmed over the whole composition range. The lattice parameters showed a linear variation with increasing x which can be well correlated with the ionic radius of the RE³⁺ ions.     

Magnetic entropy change in the monovalent doping La<Subscript>0.7</Subscript>Ba<Subscript>0.2</Subscript>M<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> (M = Na,Ag, K) manganites

Structural, magnetic, and magnetocaloric properties of monovalent doped La_0.7Ba_0.2M_0.1MnO₃ (M = Na, Ag, K) powder samples, synthesized using the solid state reaction at high temperature, have been experimentally investigated. The Rietveld refinement of the X-ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with space group. Lattice parameters and the unit cell volume increases with increasing average A-site ionic radius 〈r _A〉. The Mn–O–Mn bond angle decreases with increasing 〈r _A〉, ranging from 168.32° (M = Na) to 165.91° (M = K). All our studied samples undergo a paramagnetic–ferromagnetic transition. The Curie temperature T _C, shifts slightly to a lower temperature with increasing 〈r _A〉, which is consistent with large cationic disorder. Magnetic entropy change, , deduced from isothermal magnetization curves, reaches 3.04, 3.14, and 3.01 J/kg K for M = Na, Ag, and K, respectively, in a magnetic applied field change of 5T. Large relative cooling power (RCP) value of 337.9 J/kg is obtained for La_0.7Ba_0.2K_0.1MnO₃ sample, at a field change of 5T. This relatively large value associated to a Curie temperature of 311.5 K makes the present compound a promising candidate for the magnetic refrigerators around room temperature.