The solid solutions of BiFeO3–BaTiO3 (BFO − BTO) with the composition in the morphotropic phase boundary (MPB) were synthesized for piezo-photocatalytic application. The MPB samples were exploited for such an application because they have two special properties, i.e., a large piezoelectric effect and the coexistence of both BFO and BTO phases. BFO has a small bandgap for efficient absorption of sunlight, but its conduction band potential is too high for photoexcited electrons to produce superoxide radicals. In contrast, despite a large bandgap, BTO has its conduction and valence band potentials both located properly for photoexcited electrons and holes to produce superoxide and hydroxyl radicals. Piezoelectric modulation of band structures allows both BFO and BTO phases to take their advantages. Methylene blue (MB) was used as a model pollutant for various catalytic processes. In sole piezocatalytic action, a degradation efficiency of 86

Si-doped WO3 films with Pd surface decoration were deposited by RF magnetron sputtering for isoprene sensing. A few decoration processes were attempted to achieve best sensing performance. Although Pd decoration induced a negligible change in X-ray diffraction patterns, a variation in band gap was observed, due to an increased number of oxygen vacancies in the films as revealed by X-ray photoelectron spectroscopy, which also indicated that Pd was partially oxidized. Transmission electron microscopy confirmed that the film surface was covered by a layer of Pd nanoparticles, which had the Pd/PdO core-shell nanostructure with a size of 5-10 nm. Sidoped WO3 films with 0.64/1 Pd decoration exhibited excellent isoprene response, measuring 43.8 for 5 ppm isoprene and 8.03 for 0.7 ppm isoprene at a working temperature of 350 degrees C. The films showed an extremely short isoprene response time of about 0.4 s. Moreover, the films showed a good selectivity, with the sensor response of isoprene being 2.3, 7.0, 7.4, 16.9, and 20.6 times higher than that of ethanol, methanol, acetone, CO2, and CO, respectively.

(Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 (NBBSCT) high-entropy ceramics were synthesized by solid-state sintering in air at about 1200 degrees C. A high degree of disorder caused by multiple A-site occupations with equal fractions of elements gave rise to enhanced relaxor behavior, resulting in a smaller remnant polarization (Pr) compared to samples with unequal fractions of A-site elements. Further B-site substitution of Ti4+ with isovalent Zr4+ reduced Pr even more due to the extra disorder at the B-site, as well as a notable lattice strain indicated by the Williamson-Hall analysis of X-ray diffraction data. Doping Zr4+ up to 20 at% led to an increase in dielectric breakdown strength while causing a reduction in maximum polarization (Pmax). Extra co-doping at the B-site with 1.25 at% aliovalent Ga3+ and Nb5+ regained a high Pmax, measuring 32.78 mu C/cm2 under an applied electric field of 500 kV/cm. The calculated recoverable energy density (Wrec) was 6.38 J/cm3 with an efficiency of 81.2 %, which was high among the reported Wrec for high-entropy ceramics. The samples showed a very fast discharge rate. With a 200 Ohm load resistor, 90 % of the stored charges could be released in around 300 ns. The electric polarizations of the samples exhibited high thermal stability and excellent fatigue property that showed minimal deterioration after 105 testing cycles.

Si-doped WO3 films were sputtered at room temperature and then annealed in air at 500 degrees C. The Si doping resulted in structural distortion from space group P21/n to Pc. A high density of pores with a diameter of similar to 20 nm was observed in the films, which is ideal for gas sensing applications because of the easy diffusion of gas. Isoprene sensitivity, which is defined as the resistance ratio measured in pure air and in air containing 5 ppm isoprene, was greatly improved by the Si doping. The films containing 6.3 at% Si showed the highest sensitivity of 7.7 at a working temperature of 325 degrees C. However, despite a lower sensitivity of 6.9 measured at 350 degrees C, the films exhibited better gas selectivity for isoprene over a range of reference gases, including methanol, ethanol, acetone, CO and CO2. The response and recovery times of the films were very short, being less than 1.5 and 3.0 seconds, respectively. Detailed characterization with a range of techniques verified that the increase in gas sensitivity in the Si-doped films was related to better oxygen adsorbability as a consequence of an increase in positively-charged oxygen vacancies introduced by the aliovalent substitution of W6+ by Si4+.

BiFeO3 (BFO) was mixed with BaTiO3 (BTO) to form a solid solution of large piezoelectric coefficient (d(33)) for the fabrication of magnetoelectric (ME) composites with the Zn-doped CoFeO4 (CFO). The 0.67BFO+0.33BTO solid solution, which was doped with 1 at% MnO2 for lowering leakage current, showed a high d(33) of 121 pC/N. However, in the composites made with CFO, a much lower d(33) (<42 pC/N) was retained. The microstructure of the composites was featured by the large CFO grains (similar to 5 mu m) embedded in the 0.67BFO+0.33BTO matrix of much finer grains (similar to 0.5 mu m). The CFO grains each had a well-defined morphology with clear boundary discriminating them from the neighboring piezoelectric phase. Both the CFO and piezoelectric grains showed a high crystallinity as indicated by the appearance of clear Kikuchi patterns in electron backscattered diffraction. After reducing DC conductivity of CFO by Zn-doping and the optimization of fractional ratio of the Zn-doped CFO in the composites, a ME voltage coefficient of 81.8 mV/cm-Oe was achieved, which was high among the lead-free particulate ME composites prepared by the conventional solid-state sintering.

Thin films of BiFeO3 (BFO) were grown on a LaNiO3 buffered glass substrate by RF magnetron sputtering. The deposition parameters were tailored for the films to exhibit either n-type or p-type conductivity, which allowed the fabrication of a BFO p-n junction for photocatalytic applications. Both p/n-type films contained oxygen vacancies with the atomic fraction being 7.7% and 2.0%, respectively. The p-type conductivity was correlated to the positively charged oxygen vacancies, which occurred in large numbers in the p-type films due to charge compensation for a higher Fe2+/Fe3+ ratio. In contrast, more oxygen vacancies in the n-type films were neutral oxygen vacancies, which were shallow electron donors. The n-type films showed a bandgap of 2.57 eV, which was slightly larger than that of the p-type films (2.50 eV). The band alignment between the p/n-type films was established based on the results of ultraviolet photoelectron spectroscopy. The Fermi level of both p/n-type films was close to the middle of the bandgap as a result of low carrier concentrations, which were consistent with the carrier concentrations calculated from the slope of the Mott-Schottky plot. The BFO p-n junction allowed a fast separation of photo-generated charge carriers as confirmed by the observation of a great increase in photocurrent, which led to a great improvement in photodegradation of methylene blue (MB). The BFO p-n junction could degrade 95.5% MB in 120 min (10 x 10 mm(2) film in 20 mL of 10 mg L-1 MB) and the degradation efficiency remained above 90.3% after five cycles of reuse.

BiFe1−2xMnxMgxO3 (BFMM, x = 0−8%) was mixed with exfoliated g-C3N4 (GCN) to form a composite for establishing an S-scheme heterojunction for photodegradation. BFMM was synthesized by sol–gel method, and showed a decreased band gap from 2.24 eV to 1.75 eV as x increased from 0% to 7%, allowing a more efficient absorption of sunlight. GCN was prepared by thermal polymerization of melamine and then exfoliated to form nanosheets by sulfur acid in order to increase the specific surface area and thus increase reaction sites. A composite with a weight ratio of BFMM/GCN equal to 1 : 3 was prepared by sintering the powder mixture at 300 °C. Such a composite showed a greatly improved efficiency in photodegradation of methylene blue, which was over 6 times faster than pristine BiFeO3, and the Mn/Mg co-doping improved the efficiency by 48%. The Mott–Schottky plots showed that both GCN and BFMM are n-type semiconductors with flat-band potentials of −0.79 and +0.11 V (vs. NHE), respectively. So, the band alignment allowed the S-scheme to work, leading to an efficient separation of photogenerated electrons and holes, which was confirmed by the greatly increased photocurrents measured with the composites.

(1-x)(0.3BiFeO(3)-0.7SrTiO(3))-xK(0.5)Na(0.5)NbO(3) (BFO-STO-xKNN, x=0-0.05) ceramics were synthesized by solid state sintering for energy storage application. The grain size of BFO-STO-xKNN increased with KNN content until x=0.01 and then decreased as x increased further. In contrast, the lattice parameter of BFO-STO-xKNN decreased initially with KNN addition and then increased as x increased further. The initial decrease in lattice parameter was explained by the reduced chemical expansion associated with oxygen vacancies, while the latter increase was due to larger ionic sizes of the dopants. The dielectric response in samples without KNN addition resulted from the Maxwell-Wagner effect with the occurrence of a low frequency (500 Hz) peak at room temperature, while the dielectric relaxation in KNN added samples appeared to have the Debye type with the relaxation peak occurring at a high frequency beyond 10(6) Hz. The BFO-STO samples free of KNN showed a finite DC conductivity due to electronic hopping between Fe2+/Fe3+, which was absent in KNN added samples, and hence they showed extremely low DC conductivity. KNN-added BFO-STO exhibited slim hysteresis loops ideal for energy storage application. A high recoverable energy density (W-rec) of 3.20 J/cm(3) with 88.0% efficiency (eta) was achieved with the x=0.01 samples at the applied field of 273 kV/cm. The x=0.01 samples also showed good thermal stability of W-rec and eta, which varied only 4.0% and 0.8%, respectively, over the temperature range between 25 and 100 ?C.

Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu2+/Eu3+ and Ti4+/Ti3+ in EuTiO3 and Eu0.7Ba0.3TiO3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co2+/Ni2+ in Eu0.7Ba0.3TiO3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti3+ numbers and an increase in Eu3+ numbers. On the other hand, Ba2+ doping led to an increased lattice parameter due to its larger ionic size than Eu2+, whereas the Co2+/Ni2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu0.7Ba0.3TiO3 exhibited a clear ferroelectricity, which persisted in the Co2+/Ni2+ co-doped samples until the doping levels of y = 0.05 and 0.10, respectively. Eu0.7Ba0.3TiO3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co2+/Ni2+ turned the samples from antiferromagnetic to ferromagnetic with transition temperatures of 2.98 K and 2.72 K, respectively. The cause for such a transition could not be explained by the larger lattice volume, oxygen vacancies and mixed valences of Eu2+/Eu3+, which were proposed in previous works. Instead, it was more likely to arise from a large asymmetric distortion of the Eu–O polyhedron introduced by the aliovalent doping, which promotes the admixture of Eu 5d and 4f states.

CoFe2O4-K0.5Na0.5NbO3 (CFO-KNN) composites were sintered in air at 1100 degrees C for 2 h. The relative density of sintered CFO-KNN varied with the KNN/CFO ratio and when the volume fraction of KNN reached 50% or more, the sintered composites had a relative density higher than both of the components (i.e., individually sintered KNN and CFO). The highest relative density (94%) was obtained with the composites of 80 vol% KNN. Transmission electron microscopy did not observe any secondary phase at the interface between CFO and KNN grains. However, elemental analyses showed traces of interdiffusion of Na, K, Co, and Fe ions, which were within the solubility limit of both lattices so that no segregation of other phase occurred. Nevertheless, the interdiffusion altered grain growth kinetics for both phases, resulting in the changes in grain sizes for both KNN and CFO in the composites. The composites of higher CFO content showed lower piezoelectric d(33) due to a higher DC conductivity that resulted in an incomplete poling of samples. The attainable magnetoelectric voltage coefficient was 3.6 mV cm(-1) Oe(-1), which was measured with the composites of 50 vol% KNN.

BiCuSeO epitaxial films were grown on (001)/(110) SrTtO(3) (STO) substrates by RF magnetron sputter deposition. A sputter power over 40 W was needed to transfer target composition to substrate, leading to a fast deposition rate over 17.5 nm/min. The films grown on (001) STO at 100 150 degrees C showed a dominant [110] orientation instead of [001], which was what expected in view of the smallest lattice misfit and perfect match in symmetry between (001) BiCuSeO and (001) STO. This was caused by slow film growth along c-axis that could not follow the fast deposition rate, whereas a fair lattice misfit, combined with strong bonding along directions vertical to c-axis, entails the growth along [110] at low temperature. Preferred [001] orientation only occurred at high temperature (>350. C) when the kinetic process was accelerated. However, high temperature and the fast deposition rate imposed by the required sputter power led to the growth of multiple orientations. Epitaxial growth of (001) BiCuSeO film on (001) STO was achieved after the deposition rate was reduced to 0.67 nm/min by a periodically opening and closing shutter installed in front of sputter target. Interestingly, (001) BiCuSeO epitaxial film could be grown on (110) STO at a fast deposition rate of 15 nm/min. Such films on (110) STO had to be grown at higher temperature (similar to 500 degrees C). In contrast to (001) STO, (110) STO did not had good lattice match with any BiCuSeO orientation other than [001], so fast kinetic process only promoted the growth of single [001] orientation.

La and Y doped SrTiO3 (STO) thin filmswere grown on (100) oriented pure STO single crystal substrates by the RF magnetron sputter technique. The La/Y doped layer is intended for use as bottom electrode for epitaxial growth of various functional oxide films. The results showed that one of the crucial deposition parameters to achieve the epitaxial growth of La/Y doped STO films with a pure phase and good electrical conductivity was sputter power, which must exceed 120 W. The conductivity of the grown films increased with the increase in sputter power and the La0.1Sr0.9TiO3 (LSTO) films deposited at 200 W had the highest conductivity of 292 S/cm. This was ascribed to the increased percentage of Ti3+ ions in the sputtered films, which was confirmed by the X-ray photoelectron spectroscopy. LSTO films deposited at 130 W were (100) oriented but the increased sputter power promoted the growth of a second texture, i.e. (110). On the other hand, Y0.08Sr0.92TiO3 (YSTO) films were able to keep the unique (100) texture in the films deposited over a range of sputter powers up to 200 W, although the conductivity of YSTO was lower, which was 98.0 S/cm for the films sputtered at 200 W. (c) 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized from chemical solution via hydrothermal route at 200 degrees C. However, for many applications, ceramic samples of reasonable bulk density (>80%) have to be sintered at temperature over 700 degrees C, which in this case results in a significant reduction in resistivity due to increased amounts of Fe2+. Interestingly, doping of a few percent Sb minimized such a problem and the sintered Sb:BFO ceramics retained a similarly high resistivity as samples cold-pressed from the chemical-solution synthesized powders. However, for cold-pressed samples, Sb:BFO actually had higher conductivity than undoped BFO. Temperature-dependent conductivity showed that cold-pressed samples of both undoped and Sb doped BFO had the similar activation energy of 1.0 eV, typical for electrons trapped in oxygen vacancies. After sintering, the activation energy of Sb:BFO remained almost unchanged, but the activation energy of undoped BFO changed to 0.4 eV, which is associated to electron hopping between Fe2+/Fe3+. X-ray photoelectron spectroscopy (XPS) showed a significant increase in Fe2+/Fe3+ ratio from 6.6/93.4 to 25.7/74.3 in undoped BFO after sintering, while for 1% Sb doped BFO the increase was much milder from 10.9/89.1 to 14.1/85.9. XPS also showed that Sb had single +3 oxidation state before sintering, but after sintering a fairly large portion of Sb5+ occurred. So, charge compensation for oxygen vacancies in undoped BFO was achieved dominantly by reduction of Fe3+ to Fe2+, while in Sb:BFO it was achieved more by cation vacancies. (C) 2018 Elsevier B.V. All rights reserved.

Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) composite films were co-sputtered on (001) SrTiO3 (STO) substrates, which were confirmed to be epitaxial by both 1D and 2D X-ray diffractions. Conductive LaNiO3 (LNO) was sputtered on STO as bottom electrode for magnetoelectric (ME) measurement across film. The LNO layer was epitaxial and composed of nanocolumns perpendicular to substrate, which are helpful in reducing "substrate clamp" effect because of the flexibility of nanocolumns. NZFO + BFO films co-sputtered on LNO/STO were also epitaxial but both out-of-plane and in-plane textures of BFO were degraded with full width at half maximum of 1.974 degrees and 2.55 degrees, respectively, compared to 1.163 degrees and 1.71 degrees in films grown on bare STO. There were apparent tetragonal distortions in NZFO and BFO due to compressive in-plane strains imposed by epitaxial growth of larger NZFO and BFO lattices on smaller LNO lattice. Transmission electron microscopy (TEM) showed that the composite films were compact with clear boundaries between the NZFO and BFO phases, which were uniformly distributed with the ratio of about 35% NZFO and 65% BFO. Cross-sectional TEM revealed that crystallographic planes were very well aligned between BFO and LNO, but NZFO planes tilted 7.5 degrees due to large lattice misfit. When measured vertically from LNO to top surface of composite film, large ME voltage coefficient at zero bias field was observed, which was 911 mVcm(-1) 1Oe(-1) at the frequency of 8 kHz. This was ascribed to the large heteroepitaxial strains in composite films. (C) 2017 Elsevier B.V. All rights reserved.

Rare-earth iron garnets (RIG, R = Y, Tb and Lu) were sintered at 1350 degrees C. Their crystal structures were refined by the Rietveld method, which showed that the oxygen coordination polyhedra were highly distorted. X-ray photoelectron spectroscopy revealed a similar Fe2+/Fe3+ ratio (similar to 27/73) in different RIGs. The origins of dielectric responses were identified by cross examination of the permittivity, modulus and impedance presentations. Fitting experimental data with the Debye-type and Maxwell-Wagner models revealed that the dielectric relaxation at room temperature was dominated by the Debye-type process but as temperature increased, the Maxwell-Wagner effect gradually took over. The static permittivity was 750, 785 and 2653 for YIG, TbIG and LuIG, respectively. The particularly large permittivity of LuIG arose from a large difference between the distortions of FeO6 and FeO4 in the structure and therefore, a large dipole moment was created when electron hopping between the octahedral and tetrahedral sites took place. (C) 2016 Elsevier B.V. All rights reserved.

Multiferroic composite films of Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) were deposited on Si and LaNiO3 (LNO) buffered Si substrates at 700 °C, by co-sputtering from two individual targets of the components.

J. Am. Ceram. Soc., 97 [7], 2185-2194 DOI: 10.1111/jace.12960 (2014). There is an error in Fig. 5 and 6. The figures are interchanged. The dielectric data that appear in Fig. 5 are actually the data for samples sintered at 500°C, so should appear in Fig. 6. Also, the dielectric data shown in Fig. 6 are actually the data for samples sintered at 400°C, so should be in Fig. 5. The corrected figures appear below.