Glass‐Like Thermal Conductivity of (010)‐Textured Lanthanum‐Doped Strontium Niobate Synthesized with Wet Chemical Deposition

We have measured the cross‐plane thermal conductivity (κ) of (010)‐textured, undoped, and lanthanum‐doped strontium niobate (Sr_2?xLa_xNb₂O_7?δ) thin films via time‐domain thermoreflectance. The thin films were deposited on (001)‐oriented SrTiO₃ substrates via the highly‐scalable technique of chemical solution deposition. We find that both film thickness and lanthanum doping have little effect on κ, suggesting that there is a more dominant phonon scattering mechanism present in the system; namely the weak interlayer‐bonding along the b‐axis in the Sr₂Nb₂O₇ parent structure. Furthermore, we compare our experimental results with two variations of the minimum‐limit model for κ and discuss the nature of transport in material systems with weakly‐bonded layers. The low cross‐plane κ of these scalably‐fabricated films is comparable to that of similarly layered niobate structures grown epitaxially.     

Chloride flux growth of crystalline strontium niobates and nitridation to perovskite SrNbO2N

Highly crystalline (110) layered perovskite Sr₂Nb₂O₇, (111) layered perovskite Sr₅Nb₄O₁₅ and complex perovskite Sr₄Nb₂O₉ were prepared by NaCl-KCl flux growth method from SrCO₃ and Nb₂O₅. This flux synthesis achieves single strontium niobate phase in contrast to mixed niobates from the solid state reaction with the same heating parameters. A little excess of Sr source was found to be required for the synthesis of Sr₅Nb₄O₁₅ and Sr₄Nb₂O₉ at elevated temperature due to slight evaporation. The three strontium niobates were converted to perovskite SrNbO₂N via thermal ammonolysis under NH₃ flow at 900 °C. Post-wash treatment was performed to remove the byproduct SrO. This makes additional nanopores in SrNbO₂N in the cases of Sr₅Nb₄O₁₅ and Sr₄Nb₂O₉, and results in increasing surface areas of SrNbO₂N with Sr:Nb ratios in the precursors (from 9.9 to 19.8 and 35.5 m²/g). On the other hand, the UV–Vis diffusion reflectance spectra reveal decreasing light absorption by defects in SrNbO₂N in this order. This suggests fewer low-valent Nb defects in SrNbO₂N prepared from precursor with higher Sr:Nb ratio. SrNbO₂N prepared from Sr₄Nb₂O₉ would be advantageous for applications that require high surface area and low defect density of the material.     

Electrical and Optical Properties of Transparent Conducting p‐Type SrTiO3 Thin Films

We report a systematic study of the electrical and optical properties of epitaxial perovskite p‐type In‐doped SrTiO₃ thin films (SrIn_xTi_1?xO₃, 0 ≤ x ≤ 0.15) grown on single‐crystal (100)‐oriented LaAlO₃ substrates using a hybrid method which combines pulsed laser deposition and molecular beam epitaxy in a range of deposition conditions. X‐ray diffraction analysis confirms the epitaxial growth of high crystal quality films. Four‐point probe and Hall Effect measurements demonstrate that the films are p‐type semiconductors with a low resistivity of ~10^?2 Ω·cm and a high carrier concentration of ~10¹⁹ cm^?3. The optical transmittance spectra reveal that the films are highly transparent (?70%) in the visible region.     

Structure and conducting properties of La1-xSrxCoO3-δ films

La_1-xSr_xCoO_3-δ (LSCO) films have been deposited on LaAlO₃ (LAO), La_1-xSr_xGa_1-yMg_yO_3-δ/LaAlO₃ (LSGM/LAO) and yittria-stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell cathodes. The optimum conditions for deposition were determined for the different substrates in an ambient of 80–310 mTorr oxygen pressure and at a substrate temperature range of 450 to 750°C. The films structures were analyzed by XRD, RBS and SEM. Epitaxial LSCO films were grown with (110) preferred orientation on YSZ, and with (100) orientation on LAO and LSGM/LAO. The electrical resistivity of the epitaxial LSCO films ranged from 10⁻² to 10⁻⁴ Ω cm, depending on the deposition temperature and substrate. The ionic conducting behavior of the LSCO film on YSZ was investigated by impedance measurement.     

Effects of niobium doping site and concentration on the phase structure and oxygen permeability of Nb-substituted SrCoOx oxides

Niobium doping effect on phase structure, phase stability and electrical conductivity of SrCoO_x oxides and oxygen permeability of the corresponding membranes were systematically investigated. Niobium was successfully incorporated into A-site, B-site or simultaneously A and B double sites of SrCoO_x oxide and stabilized the perovskite structure with a cubic symmetry in air down to room temperature at a proper doping amount. However, the A-site doping could not stabilize the cubic structure under a more reducing atmosphere of nitrogen, as to SrCo_1?yNb_yO_3?δ, y ≥ 0.1 is necessary to sustain the cubic perovskite structure. Simultaneous doping of Nb at A and B sites is the most effective way to stabilize the perovskite structure under nitrogen atmosphere. Irrespective of doping site, the electrical conductivity decreased monotonously with Nb-doping amount. Both Nb_xSr_1?xCoO_3?δ and Nb_zSr_1?zCo_1?zNb_zO_3?δ envisaged a decrease in oxygen permeation flux with Nb-doping amount while SrCo_1?yNb_yO_3?δ reached the maximum flux at y = 0.1. Among all the membranes, SrCo_0.9Nb_0.1O_3?δ and Nb_0.05Sr_0.95Co_0.95Nb_0.05O_3?δ show the highest oxygen fluxes of 3.5 and 2.7 ml cm^?2 min^?1 at 900 °C under an air/helium gradient, respectively.     

Enhanced Thermoelectric Properties in Cu‐Doped c‐Axis‐Oriented Ca3Co4O9+δ Thin Films

Highly c‐axis‐oriented Ca₃Co_4?xCu_xO_9+δ (x = 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO₃ (001) single‐crystal substrates. X‐ray diffraction, field‐emission scanning electronic microscopy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ with quadruplicated rock‐salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu‐doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu‐doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu‐doped Ca₃Co₄O_9+δ thin films could be a promising candidate for thermoelectric applications.     

Sodium Doping Effects on Layered Cobaltate Bi2Sr2Co2Oy Thin Films

Highly c‐axis oriented Bi_2?xNa_xSr₂Co₂O_y (x = 0, 0.1, 0.2, 0.3) thin films were successfully deposited onto LaAlO₃ (0 0 1) single crystal substrates by the chemical solution deposition method. The Na‐doping effects on microstructures as well as transport and thermoelectric properties were investigated. The crystallite size normal to the thin film surface was decreased with Na doping, and the carrier concentration and mobility was enhanced and decreased, respectively. As for the transport properties, it is suggested that Na‐doping‐induced disorders play a more important role at low temperatures, while at the medium temperature the doping play a trivial role, at higher temperatures Na‐doping weakens the electron correlation. Combined with the transport properties and Seebeck coefficient results, it is suggested that the thermoelectric properties are mainly controlled by carrier concentration due to the hole doping in blocking layers. Power factor at 300 K was enhanced about 22% for the Bi_1.7Na_0.3Sr₂Co₂O_y thin film as compared with that of the undoped thin films, suggesting that Na doping at blocking layer in Bi₂Sr₂Co₂O_y was an effective route to enhance the thermoelectric power factor.     

Effect of Substrate on Structure and Multiferrocity of (La,Mn) CoSubstituted BiFeO3 Thin Films

In this article, we report the substrate effect on ferroelectric and magnetic properties of epitaxial BiFeO₃‐based thin films at room temperature. (La, Mn) cosubstituted BiFeO₃ (BFOLM) thin films were deposited on differently lattice mismatched single‐crystal substrates to manipulate the strain states in the as‐deposited films. All the films with 30‐nm thick CaRuO₃ bottom electrodes exhibited highly epitaxial growth behavior with a slightly monoclinic distorted lattice structure while their strain states are drastically different as confirmed by X‐ray reciprocal space mapping. These films possessed significantly different macroscopic ferroelectric properties with giant remanent polarization of 101 ± 2, 65 ± 2, and 48 ± 2 μC/cm² for the films grown on SrTiO₃, (La, Sr)(Al, Ta)O₃, and LaAlO₃, respectively. It is found that the room‐temperature magnetic properties are also in accordance with their strain state, having a reciprocal relationship with polarization. For example, the enhanced magnetization is associated with the suppressed polarization and vice versa. The stain tunability of multiferroic properties in BFOLM thin films are presumably ascribed to the polarization rotation and oxygen octahedral tilts.     

Crystallographic Orientation Dependence on Electrical Properties of (Bi,Na)TiO3‐based Thin Films

Orientation‐engineered (La, Ce) cosubstituted 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ thin films were epitaxially deposited on CaRuO₃ buffered (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.35 single‐crystal substrates by pulsed laser deposition. The ferroelectric, piezoelectric, dielectric, and leakage current characteristics of the thin films were significantly affected by the crystallographic orientation. We found that the (001)‐oriented film exhibited the best ferroelectric properties with remnant polarization P_r = 29.5 μC/cm² and coercive field E_c = 7.4 kV/mm, whereas the (111)‐oriented film demonstrated the largest piezoelectric response and dielectric permittivity. The bipolar resistive switching behavior, which is predominantly attributed to a combined effect of ferroelectric switching and formation/rupture of conductive filaments, was observed. The conduction mechanisms were determined to be ohmic conduction and Poole–Frenkel emission at high‐ and low‐resistance states, respectively, in all the films.     

Effect of Fe Doping on Layered GdBa0.5Sr0.5Co2O5+δ Perovskite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Layered perovskite cathode materials have received considerable attention for intermediate temperature solid oxide fuel cells (IT‐SOFCs) because of their fast oxygen ion diffusion through pore channels and high catalytic activity toward the oxygen reduction reaction (ORR) at low temperatures. In this study, we have investigated the effects of Fe substitution for the Co site on electrical and electrochemical properties of a layered perovskite, GdBa_0.5Sr_0.5Co_2?xFe_xO_5+δ (x = 0, 0.5, and 1.0), as a cathode material for IT‐SOFCs. Furthermore, electrochemical properties of GdBa_0.5Sr_0.5CoFeO_5+δ–yGDC (y = 0, 20, 40, and 50 wt%) cathodes were evaluated to determine the optimized cell performance. At a given temperature, the electrical conductivity and the area‐specific resistances (ASRs) of GdBa_0.5Sr_0.5Co_2?x Fe_xO_5+δ decrease with Fe content. The lowest ASR of 0.067 Ω·cm² was obtained at 873 K for the GdBa_0.5Sr_0.5CoFeO_5+δ. The GdBa_0.5Sr_0.5CoFeO_5 + δ composite with 40 wt% GDC was identified as an optimum cathode material, showing the highest maximum power density (1.31 W/cm²) at 873 K, and other samples also showed high power density over 1.00 W/cm².     

Filled oxygen‐deficient strontium barium niobates

Filled strontium barium niobate (SBN, Sr_xBa_6?xNb₁₀O_30?δ) compositions from the barium end‐member to a Sr:Ba ratio of 80:20 were fabricated using conventional sintering under oxygen‐deficient conditions. Single‐phase specimens were obtained when sintered at 1350°C under a reducing condition of about 1.0 × 10^?16 atm pO₂. X‐ray diffraction and energy dispersive spectroscopy using scanning electron microscopy and transmission electron microscopy were used to confirm the phase‐purity. Lattice parameters derived from Rietveld refinements were used to trace Vegard's Law over the solid solution. It was found that Vegard's Law is followed over two ranges, which is believed to be due to preferential site occupancy of the A sites as the Sr content changes. The successful fabrication of filled SBN bronzes provides an avenue for correlating trends in electrical characteristics of the SBN solid solution.     

Dielectric and mechanical characteristics of lanthanum aluminate ceramics with strontium niobate addition

The microstructures, microwave dielectric properties and mechanical properties were investigated for LaAlO₃ ceramics with Sr₂Nb₂O₇ additive. The grain size decreased significantly when the additive was introduced, and the Sr₂Nb₂O₇ reacted with the LaAlO₃ ceramic matrix to form a LaNbO₄ secondary phase. The dielectric constant varied slightly, while the Qf value increased at first and then decreased when the additive content passed a critical value. The effects of the Sr₂Nb₂O₇ additive upon the temperature coefficient of resonant frequency were dependent on the sintering conditions. The fracture toughness was significantly improved by Sr₂Nb₂O₇ addition.     

The Effect of Barium Substitution on the Ferroelectric Properties of Sr2Nb2O7 Ceramics

This work revealed that the solid solution compounds of Sr_{2 ? x}Ba_xNb₂O₇ are promising lead‐free materials for high‐temperature piezoelectric sensor application. These compounds were confirmed as ferroelectric materials with high Curie points ( > 900°C) by their piezoelectric activity after poling, ferroelectric domain switching in their P–E hysteresis loops and thermal depoling behavior. The effect of Ba substitution on the structure and properties of Sr_{2 ? x}Ba_xNb₂O₇ (x  <  1.0) was investigated. The solid solution limit of Sr_{2 ? x}Ba_xNb₂O₇ was determined by XRD as x < 0.6. The a‐, b‐, c‐ axes, and cell volume increase with Ba addition. The textured ceramics of Sr_{2 ? x}Ba_xNb₂O₇ were prepared for the first time. The highest d₃₃ was measured as 3.6  ±  0.1 pC/N for Sr_1.8Ba_0.2Nb₂O₇.     

Chemical Bulk Diffusion Coefficient of a La0.5Sr0.5CoO3−δ Cathode for Intermediate‐Temperature Solid Oxide Fuel Cells

In the first part of this study, the characteristics of a La_0.5Sr_0.5CoO_3?δ cathode are described, including its chemical bulk diffusion coefficient (D_chem), and electrical conductivity relaxation experiments are performed to obtain experimental D_chem measurements of this cathode. The second part of this study describes two methods to improve the single‐cell performance of solid oxide fuel cells. One method uses a composite cathode, i.e., a mix of 30 wt% electrolyte and 70 wt% cathode; the other method uses an electrolyte‐infiltrated cathode, i.e., an active ionic‐conductive electrolyte with nano‐sized particles is deposited onto a porous cathode surface using the infiltration method. In this work, 0.2M Ce_0.8Sm_0.2O_1.9 (SDC)‐infiltrated La_0.5Sr_0.5CoO_3?δ exhibits a maximum peak power density of 1221 mW/cm² at an operating temperature of 700°C with a thick‐film SDC electrolyte (30 μm), a NiO + SDC anode (1 mm) and a La_0.5Sr_0.5CoO_3?δ cathode (10 μm). The enhancement in electrochemical performances using the electrolyte‐infiltrated cathode is attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the number of electrochemical sites available for the oxygen reduction reaction.     

Strong Effect of Oxygen Partial Pressure on Electrical Properties of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films

0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT) epitaxial thin films were grown on SrRuO₃ (SRO) coated (001)‐oriented SrTiO₃ (STO) single crystal substrates by pulsed laser deposition under different oxygen partial pressures in the processing of deposition. The effects of oxygen partial pressure on structure, cation stoichiometry, surface morphology, leakage current behavior, ferroelectric, and piezoelectric properties were investigated. Both the lattice parameters and (Ba + Ca)/(Ti + Zr) cation ratio decrease with increasing oxygen partial pressure. The BCZT thin film with the ideal cation stoichiometry was obtained under 200 mTorr, giving rise to a remanent polarization P_r = 14.5 μC/cm² and effective piezoelectric coefficient d₃₃ = 96 ± 5 pm/V.     

Relationship between distortion of crystal structure and dielectric properties of complex perovskite oxide Ba(Co,Zn)1/3Nb2/3O3 thin films

The oxygen octahedral can be distorted by epitaxial strain due to the lattice mismatch. The epitaxial strain (ε_yy) linearly decreases from ? 0.244% to ? 0.445% with the growth temperature. Thin films grow along c axis on the SrTiO₃ substrate and exhibit the epitaxial relationship of Ba(Co,Zn)_1/3Nb_2/3O₃ (001) // SrTiO₃ (001). The superlattice reflections arising from in-phase tilting of the oxygen octahedra are clearly visible along [010] and [111] zone axis. The IR modes at 330 cm^?1 and 390 cm^?1 related to in-phase tilting are observed in far-infrared reflectivity spectroscopy. The calculated Q×f values from far-infrared reflectivity spectra of films grown at 550 °C to 700 °C increases from 51,000 GHz to 91,000 GHz mainly due to the enhancement of crystalline quality. The intrinsic quality factor (Q) is mainly contributed by O-(Co, Nb)-O and O-(Zn, Nb)-O bonding modes, while in-phase tilting in BCZN films may result in enhanced dielectric constants.     

Orientation Growth and Magnetic Properties of BaM Hexaferrite Films Deposited by Direct Current Magnetron Sputtering

In‐plane c‐axis oriented Ba‐hexaferrite (BaM) thin films were prepared on a‐plane sapphire (Al₂O₃) substrates using direct current (DC) magnetron sputtering followed by ex‐situ annealing. The sputtering atmosphere was found to have a great influence on the stoichiometry, orientation growth, and grain morphology of the as‐prepared BaM films. With moderate oxygen partial pressure during sputtering, in‐plane c‐axis highly oriented BaM films were obtained. The films showed strong magnetic anisotropy with a high hysteresis loop squareness (M_r/M_s of 0.96) along in‐plane easy axis and a low M_r/M_s of 0.05 along in‐plane hard axis. Rocking curves and pole figures were utilized to reveal the epitaxial‐like orientation relationship of the BaM films relative to the sapphire substrates, as well as the orientation growth dispersion of the hexagonal platelet‐shaped grains in BaM films.     

Textured YBCO-Film Formation by Sol–Gel Process and Post Annealing

Thick YBCO-films were prepared on single crystalline SrTiO₃(001) and LaAlO₃(001) substrates by the dip-coating process starting with Y-, Ba- and Cu-acetylacetonates. When a characteristic temperature during transformation of the precursor into YBa₂Cu₃O_x is exceeded a strong biaxial texture with FWHM = 1·2° for 1 μm thick fims results. When the O₂ partial pressure of the annealing atmosphere is lowered the characteristic temperature decreases and films with increased current density (j_c) are obtained. The values of J_c achieved for films deposited onto SrTiO₃(001) at 77 K in self field are as high as 50·000 A cm⁻² with T_cs of 90K.     

Sol–Gel‐Derived Amorphous‐MgNb2O6 Thin Films for Transparent Microelectronics

In this work, transparent amorphous‐MgNb₂O₆ thin films were fabricated on ITO/glass substrates using the sol–gel method. The change in the chemical states, as well as the optical and dielectric properties of MgNb₂O₆ films at various annealing temperatures is investigated. In this study, MgNb₂O₆ films exhibited the amorphous phase when the annealing temperature was below 600°C. From X‐ray photoelectron spectroscopy, the major parts of the films' chemical states can be indexed as Mg²⁺, Nb⁵⁺, Nb⁴⁺, and O^2?. Furthermore, the Nb⁴⁺ element can be reduced at higher annealing temperatures. The average transmission percentage in the visible range (λ = 400–800 nm) is over 80% for all MgNb₂O₆/ITO/glass samples, whereas the optical band gap (E_g) for all samples is estimated at ~4 eV. In addition, the dielectric constant was calculated to be higher than 20 under a 1 MHz AC electric field, with a leakage current density below 2 × 10^?7 A/cm² at 1 V. In this study, the fabrication procedure and experiment results of MgNb₂O₆ films are introduced for transparent microelectronics.     

Improved piezoelectricity and energy storage performance simultaneously achieved in [001]-preferentially oriented Bi0.5Na0.5TiO3–BaTiO3–BiMnO3 thin films grown on Nb-doped SrTiO3 single-crystalline substrates

The control of grain orientation by introducing Nb-doped SrTiO₃ single crystalline substrates is an effective way to improve piezoelectric and ferroelectric properties of thin films. Therefore, in this work, 0.99(0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃)–0.01BiMnO₃ thin films were coated on Pt(111)/TiO_x/SiO₂/Si(001) polycrystalline substrates and Nb-doped SrTiO₃ single crystalline substrates, respectively. The Nb-doped SrTiO₃ single crystalline substrates can affect the orientation of the BNT–BT–0.01BMO thin films, promote the grain growth, reduce the leakage current, and form an interfacial layer between the thin film and the substrate, and a comparatively larger converse piezoelectric coefficient (46.49 pm·V^?1), a high energy storage density (56.5 J cm^-3), and a high energy storage efficiency (79.4 %) were therefore simultaneously achieved in the thin films grown on Nb-doped SrTiO₃ single crystalline substrates, promising the oriented thin films broad application prospects.