Sintering behavior and dielectric properties of SiO2–BPO4 glass-fluxed ceramics

(1–x)SiO₂–xBPO₄ (x?=?23–70?wt%) glass-fluxed ceramics have been prepared by a traditional ceramic process. The phase assemblage, sintering, crystallization behavior, microwave dielectric properties and chemical compatibility with Ag/Cu have been studied. The SiO₂-rich compositions (x?=?23–50?wt%) could be well densified at ～975?°C/2?h, while the BPO₄-rich compositions demonstrated poor sinterability and porous microstructure. The SiO₂-rich compositions sintered at 975?°C/2?h contained BPO₄, low temperature cristobalite and glassy phases. Crystallization of BPO₄ occurred at lower temperature than that of SiO₂. Good combined microwave dielectric properties with ?_r?=?～5, Q?×?f?=?25,000?GHz and τ_f value of –7.3?ppm/°C could be obtained when 10?wt% TiO₂ was added after sintering at 975?°C/2?h. The x?=?23?wt% composition chemically reacted with Ag, but exhibited good chemical compatibility with Cu after sintering at 975?°C/2?h.     

Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.     

Enhanced electrical properties in Nd and Ce co-doped CaBi4Ti4O15 high temperature piezoceramics

Lead-free piezoelectric material with excellent piezoelectric properties and high Curie temperature is necessary for practical applications. In this work, (Nd, Ce) co-doped CaBi₄Ti₄O₁₅ (CBT) ceramics were prepared by the conventional solid-state reaction technique. The effect of (Nd, Ce) co-doping on the structure and resulting electrical properties of CBT ceramics was systematically investigated. The optimized comprehensive performances were obtained at x?=?0.075 with a large piezoelectric coefficient (19 pC/N), a low dielectric loss (0.073%) and a high Curie temperature (794?°C). More importantly, the ceramic also maintained a very high resistance and a low dielectric loss even at 400?°C (ρ?=?2.5?×?10⁸ Ω?cm, tan δ?=?1.96%) and the d₃₃ showed no sign of waning after annealed at 400?°C, which shows great potential for high temperature piezoelectric device applications. Related mechanisms for the enhancement of electrical properties were discussed.     

Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr_0.2Ti_0.8)O₃-(1-x)(Ba_0.7Ca_0.3)TiO₃ [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (T_R-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (T_T-C) of 110?°C. The dielectric analysis suggests that the phase transition at T_T-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A₁, E(LO) Raman mode. The saturation polarization (P_s) ≈8.3?μC/cm² and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 10⁵ cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high T_T-C (110?°C), a high dielectric constant (ε_r ≈?12,285) with low dielectric loss (0.03), good polarization (P_s ≈?8.3?μC/cm²) and large recoverable energy density (W?=?121?mJ/cm³) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.     

High temperature electrical conductivity and electrochemical investigation of La2-xSrxCoO4 nanoparticles for IT-SOFC cathode

Single-phase Ruddlesden popper of La_2-xSr_xCoO₄ nanopowders with x?=?0.7, 0.9, 1.1 and 1.3, were successfully synthesized by a modified sol-gel method. Structural stability and morphology of the prepared samples were examined using HT-XRD analysis, FE-SEM and SEM techniques. HT-XRD analysis of the samples, in the range of room temperature to 850?°C, revealed that the structure of all samples was tetragonal. The electrical conductivity measurements, in the range of room temperature to 850?°C, indicated that by increasing the temperature the electrical conductivity mechanism inverts from variable range hopping to the nearest-neighbor hopping of small polarons. In addition, it was found that by increasing Sr concentration the structure of the sintered samples becomes more stable. The electrochemical characterization was carried out using the impedance spectroscopy (EIS) measurements on symmetrical cells at three different temperatures, 650?°C, 750?°C and 850?°C. The area specific polarization resistance (ASR) of La_2-xSr_xCoO₄-CGO-La_2-xSr_xCoO₄ symmetrical cell, in oxygen flow, was obtained about 1.07, 0.35, 0.33 and 0.43 Ωcm² at 850?°C for the samples with x?=?0.7, 0.9, 1.1 and x?=?1.3, respectively. According to our EIS results, the main rate-limiting step for La_2-xSr_xCoO₄ cathode performance is the dissociation process of oxygen at the surface of cathode at 650?°C and the charge transfer limiting in the cathode/electrolyte at 750?°C and 850?°C. Our results showed that the samples with Sr contents of x?=?0.9 and x?=?1.1 can be the promising cathodes for IT-SOFC applications.     

Crystal structure,impedance and broadband dielectric spectra of ordered scheelite-structured Bi(Sc1/3Mo2/3)O4 ceramic

Bi(Sc_1/3Mo_2/3)O₄ ceramics were prepared via solid state reaction method. It crystallized with an ordered scheelite-related structure (a?=?16.9821(9)?Å, b?=?11.6097(3)?Å, c?=?5.3099(3)?Å and β?=?104.649(2)°) with a space group C12/C1, in which Bi³⁺, Sc³⁺ and Mo⁶⁺ are ?8, ?6 and ?4 coordinated, respectively. Bi(Sc_1/3Mo_2/3)O₄ ceramics were densifiedat 915?°C, giving a permittivity (ε_r) ～24.4, quality factor (Qf, Q?=?1/dielectric loss, f?=?resonant frequency) ～48, 100?GHz and temperature coefficient of resonant frequency (TCF)?～??68?ppm/°C. Impedance spectroscopy revealed that there was only a bulk response for conductivity with activation energy (E_a) ～0.97?eV, suggesting the compound is electrically and chemically homogeneous. Wide band dielectric spectra were employed to study the dielectric response of Bi(Sc_1/3Mo_2/3)O₄ from 20?Hz to 30?THz. ε_r was stable from 20?Hz to the GHz region, in which only ionic and electron displacive polarization contributed to the?ε_r.     

Higher permittivity of Ni-doped lead zirconate titanate,Pb[(Zr0.52Ti0.48)(1-x) Nix]O3, ceramics

The paper reports highest obtained dielectric constant for Ni-doped Lead Zirconate Titanate [PZT, Pb(Zr_0.52Ti_0.48)O₃] ceramics. The Ni-doped PZT ceramic pellets were prepared via conventional solid-state reaction method with Ni content chosen in the range 0–20?at%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the crystal structure of the prepared ceramics. The X-ray diffraction analysis indicated that the ceramic pellets had crystallized into tetragonal perovskite structure. A minute displacement of XRD peaks was detected in the diffraction spectra of Ni-doped PZT ceramic samples which when examined by size-strain plot (SSP) method revealed presence of homogenous strain that decreased with increase in concentration of Ni. In FTIR the maximum absorption at 597?cm^?1, 608?cm^?1, 611?cm^?1, 605 and 613?cm^?1 for Ni?=?0, 5, 10, 15 and 20?at%, respectively, confirmed the formation of perovskite structure in all the compositions and the slight shift suggests decrease in cell size on doping. The values of dielectric constant (ε′) & tanδ as a function of frequency and temperature were measured for the prepared ceramics and it revealed highest ever reported dielectric constant for Ni - doped PZT with Ni?=?5?at%. The dielectric variation with temperature exhibited a diffused type ferroelectric–paraelectric phase transition for the doped samples. Also, the maximum dielectric constant value (ε′_max) decreased while the phase transition temperature increased with increase in doping concentration of Ni. The estimated activation energy of different compositions was found to increase from 0.057 to 0.068?eV for x?=?0.00 to x?=?0.20 in ferroelectric phase. The piezoelectric, ferroelectric and magnetic properties were also investigated.     

Crystal structure and microwave dielectric properties of NaPb2B2V3O12(B=Mg,Zn) ceramics

Two low temperature sintered NaPb₂B₂V₃O₁₂ (B?=?Mg, Zn) ceramics with garnet structure were synthesized through conventional solid state reaction route and their crystal structure and microwave dielectric properties were investigated for the first time. Rietveld refinements of XRD patterns show both the compounds belong to cubic symmetry with space group Ia-3d. Observed number of Raman bands and group theoretical predictions also confirm cubic symmetry with space group Ia-3d for both NPMVO and NPZVO. At the optimum sintering temperature of 725?°C NPMVO has a relative permittivity of 20.6?±?0.2, unloaded quality factor (Q_uxf) of 22,800?±?1500?GHz (f?=?7.7?GHz) and temperature coefficient of resonant frequency +25.1?±?1?ppm/°C while NPZVO has relative permittivity of 22.4?±?0.2, Q_uxf of 7900?±?1500?GHz (f?=?7.4?GHz) and near zero temperature coefficient of resonant frequency of -6?±?1?ppm/°C at 650?°C. The relative permittivity of the compounds is inversely related to the corresponding Raman shifts.     

High-performance La-doped BCZT thin film capacitors on LaNiO3/Pt composite bottom electrodes with ultra-high efficiency and high thermal stability

Dielectric capacitors possessing large energy storage density, high efficiency and high thermal stability simultaneously are very attractive in modern electronic devices to be operated in harsh environment. Here, it is demonstrated that large energy storage density (W?～?15.5?J/cm³), ultra-high efficiency (η ～93.7%) and high thermal stability (the variation of both W from 20?°C to 260?°C and η from 20?°C to 140?°C is less than 5%) have been simultaneously achieved in the La-doped (Ba_0.904Ca_0.096)_0.9775+xLa_0.015(Zr_0.136Ti_0.864)O₃ (x?=?0.0075) lead-free relaxor ferroelectric thin film capacitors deposited on LaNiO₃/Pt composite bottom electrodes by using a sol-gel method. The good energy storage property of the thin film capacitors at x?=?0.0075 is mainly ascribed to the diversity of the structure of the nano-clusters around the three-phases coexisting component point (Ba_0.904Ca_0.096)(Zr_0.136Ti_0.864)O₃ where cubic, tetragonal and rhombohedral phases coexisted, as well as the ultra-high quality of thin film due to the utilization of the LaNiO₃/Pt composite bottom electrode, making it a promising candidate for dielectric capacitors working in harsh environments.     

Synthesis and characterization of Y (In,Mn) O3 blue pigment using the complex polymerization method (CPM)

In this paper, a new synthetic pathway is proposed for the system YIn_1-xMn_xO₃, a bright blue inorganic pigment, discovered in 2009. Blue pigment samples with increasing concentration of Mn³⁺ (x?=?0.08, 0.12 and 0.16) were prepared using the complex polymerization method (CPM) and compared with those synthesized via solid state reaction. All powders, the amorphous precursor from CPM and the starting materials for solid state method, were calcined at 1000, 1100, 1200 and 1300?°C for 12?h, and the resulting blue pigments were characterized by X-ray diffraction (XRD), colorimetric system CIE L*a*b* and Near infrared (NIR) reflectance measurements. XRD patterns and Rietveld Refinement show that the lowest temperature at which single hexagonal phase (isostructural to YInO₃) is formed is 1000?°C for CPM method and 1300?°C for conventional solid state method, respectively. The L*a*b* values demonstrate that the coloration of powders prepared by CPM exhibit temperature dependence below 1300?°C, a color shade shift from grayish blue to intense deep blue is observed when heating the samples from 1000 to 1300?°C. Blue pigments obtained by CPM have smaller particle size due to low temperatures and excellent near-infrared reflectance comparable to those by solid state method. Thus, providing advantages for application process and energy efficiency.     

Structural,electrical and relaxor properties of Sc-In solid solution in tetragonal tungsten bronze ceramics

The electrical properties of a family of tetragonal tungsten bronze (TTB) materials, Ba₆Sc_1-xIn_xNb₉O₃₀ (x?=?0.25, 0.5, 0.75), which display relaxor properties were characterised using high- and low-temperature dielectric spectroscopy. All powders were synthesised at 1250?°C (24?h)?+?1350?°C (6.5?h), while the pellets were further sintered at 1350?°C (12?h). At high temperature, the electrical conductivity in all samples is dominated by a single response, attributed to the bulk response, while the subtle asymmetry of the imaginary impedance peak suggests a minor contribution of the grain boundary response. In general, the Sc-In solid solutions samples exhibit similar electrical behaviour to the Sc compound, x?=?1 reported previously (Ceram. Int. 2016, 42, 11810–11821). At low temperature all compounds exhibit frequency dependent relaxor behaviour. With increasing the content of In, the dielectric peaks are more asymmetric and the curves flatten more at temperatures above the transition temperature. The dipole freezing temperature, T_VF, determined by Vogel-Fulcher (VF) analysis does not simply increase linearly as a function of M³⁺ (Sc³⁺,In³⁺) cation size, the extrapolation of VF-like curves results in considerably different values when compared to those found previously, since the acquired dielectric data are very sensitive to preparative conditions.     

Preparation and functional characterization of magnetoelectric Ba(Ti1-xFex)O3-x/2 ceramics. Application for a miniaturized resonator antenna

Diluted magnetic oxides attracted a great interest in the last years as materials for spintronics and magnetoelectric devices. We propose in the present paper such a magnetoelectric ceramic system for an application as miniaturized resonator antenna in GHz range. BaTi_1-xFe_xO_3-x/2 (0?≤?x?≤?0.02) polycrystalline ceramics have been produced by solid state reaction. X-ray diffraction analysis and Rietveld refinement have shown that Fe doping of BaTiO₃ lattice produces a transition from tetragonal crystalline symmetry (for x?≤?0.01) to a superposition of tetragonal and hexagonal phases for the compositions x?=?0.015 and 0.02. As result of Fe addition, the Curie temperature of BaTi_1-xFe_xO_3-x/2 ceramics exhibit a shift from 127?°C towards lower values and reaches 85?°C for x?=?0.02. A competition between weak ferromagnetic and antiferromagnetic character as a function of composition and temperature is determined both by the presence of transition metal ion and of the oxygen vacancies. Due to its electromagnetic properties, an optimized composition x?=?0.01 was used for producing a miniaturized antenna which was found to show a frequency dependent S₁₁ response similar to the simulated one.     

Ferroelectric P4mm to relaxor P4bm transition and temperature-insensitive large strains in Bi(Mg0.5Ti0.5)O3-modified tetragonal 0.875Bi0.5Na0.5TiO3-0.125BaTiO3 lead-free ferroelectric ceramics

Tetragonal phase (1–x)(0.875Bi_0.5Na_0.5TiO₃–0.125BaTiO₃)–xBi(Mg_0.5Ti_0.5)O₃ lead-free ferroelectrics were designed and fabricated by a conventional solid state route. All the specimens exhibit a tetragonal perovskite structure, and undergo a phase evolution from ferroelectric P4mm to antiferroelectric relaxor P4bm as the BMT addition increases. The critical composition x?=?0.04 makes a bridge between the both tetragonal phases, and gives a large field-induced strain of 0.30% and an adequately-large electrostrictive coefficient Q₃₃ of 0.0254?m⁴/C². To be highlighted, the field-induce strain of the composition x?=?0.04 shows an almost constant value over the temperature range of 18–100?°C, illustrating a temperature-insensitive behavior, which could be attributed to the widened gap between T_R–E and T_F–R. The temperature-insensitive large strain of the tetragonal BNT–BT–BMT composition give a promising potential for application in precision position actuators.     

Ultra-stable X9R type CaCu3-xZnxTi4.1O12 ceramics

CaCu_3-xZn_xTi_4.1O₁₂ (x?=?0.00, 0.05 and 0.10) precursor powders were prepared by the polymer pyrolysis (PP) solution method. Ultra-stable X9R type capacitor with very low loss tangent (tanδ) ~0.017 varied within a value of less than 0.05 in a wide temperature range of ?60 to 150?°C and high dielectric constants (ε^′) ~9200 with Δε′ ≤?±?15% in a wide temperature range of ?60 to 210?°C was achieved in CaCu_2.95Zn_0.05Ti_4.1O₁₂ (Zn05-1) ceramic obtained by sintering the precursor powder (x?=?0.05) at 1060?°C for 8?h. A major role for the validity of ε^′ and tanδ in these wider temperature ranges was suggested to originated from the very high grain boundary resistance (R_gb ~413,190?Ω?cm), resulting from the effect of Zn²⁺ doping and TiO₂-rich at grain boundary. With the excellent dielectric properties of (Zn05-1) ceramic, it was suggested to be applied for X8R and X9R capacitors. Interestingly, improvements of nonlinear properties with very high nonlinear coefficient (α ~ 25.94) and breakdown field (E_b~ 3146.25?V.cm^?1) values were achieved in (Zn05-1) ceramic, as well.     

Nanostructured catalysts for oxygen electroreduction based on bimetallic monoethanolamine complexes of Co(III) and Ni(II)

Oxygen reduction electrocatalysts based on the monoethanolmine complexes {[CoEtm]₂(μ-Etm)₄Ni(NO₃)₂} and {[CoEtm]₂(μ-Etm)₄Ni(NO₃)₂} + activated carbon AG-3 have been obtained by high-temperature synthesis. The nature of active centers on the synthesized electrocatalysts was described. Using potentiostatic and cyclic potentiodynamic voltammetry, the kinetic characteristics of catalysts in the oxygen electroreduction reaction were determined. Thermal decomposition of the thermally unstable complexes was described and character of the active centers formed was discussed. The optimal synthesis temperature of electrocatalysts is 600 °C in an inert atmosphere. The calculated exchange current densities for the oxygen electroreduction reaction at the catalysts in 1 M KOH at 20 °C was j ₀  = 1.01 × 10^?3 A g^?1–3.3 × 10^?3 A g^?1. The Tafel slopes of stationary polarization curves are 0.054–0.063 V for b ₁ and 0.106–0.125 V for b ₂ . The prepared electrocatalysts can be recommended only for electrochemical systems with alkaline electrolyte.     

Synthesis and characterization of PrxZr1-xSiO4 (x = 0–0.08) yellow pigments via non-hydrolytic sol-gel method

Yellow inorganic pigments Pr_xZr_1-xSiO₄ (x?=?0–0.08) have been prepared by a novel non-hydrolytic sol-gel (NHSG) method at 750?°C for 2?h. Replacing Pr⁴⁺ for Zr⁴⁺ in ZrSiO₄ increased the cell volume and changed the color from white to yellow gradually. The Si―O―Zr and Si―O―Pr bands were observed in the FT-IR spectra of xerogel, indicating it could reach homogeneous mixing at the atomic level. Therefore, it promoted the solid solution reaction between Pr and zircon at low temperature. The samples exhibit high doping limitation (x?=?0.08) and brilliant yellow hue (b^*?=?69.48) in contrast with the previously reported praseodymium zircon yellow pigments. The intense of yellow hue was increased with increasing the Pr doping content due to the increase of Pr⁴⁺/Pr³⁺ species. After applying on bisque ceramic tiles, the pigment exhibited excellent coloration, high thermal stability and low solubility in molten glazes, indicating its potential application in ceramic decoration.     

Enhanced piezoelectric properties and electrical resistivity in W/Cr co-doped CaBi2Nb2O9 high-temperature piezoelectric ceramics

W/Cr co-doped Aurivillius-type CaBi₂Nb_2-x(W_2/3Cr_1/3)_xO₉ (CBN) (x?=?0.025, 0.050, 0.075, 0.100, and 0.150) piezoelectric ceramics were prepared by the conventional solid-state reaction method. The crystal structure, microstructure, dielectric properties, piezoelectric properties, and electrical conductivity of these ceramics were systematically investigated. After optimum W/Cr modification, the CBN ceramics showed both high d₃₃ and T_C. The ceramic with x?=?0.1 showed a remarkably high d₃₃ value of ~15 pC/N along with a high T_C of ~931?°C. Moreover, the ceramic also showed excellent thermal stability evident from the increase in its planar electromechanical coupling factor k_p from 8.14% at room temperature to 11.04% at 600?°C. After annealing at 900?°C for 2?h, the ceramic showed a d₃₃ value of 14?pC/N. Furthermore, at 600?°C, the ceramic also showed a relatively high resistivity of 4.9?×?10⁵ Ω?cm and a low tanδ of 9%. The results demonstrated the potential of the W/Cr co-doped CBN ceramics for high-temperature applications. We also elucidated the mechanism for the enhanced electrical properties of the ceramics.     

In situ synthesis,mechanical properties,and microstructure of reactively hot pressed WB4 ceramic with Ni as a sintering additive

In this study, tungsten tetraboride (WB₄) ceramics were synthesized in situ from powder mixtures of W and amorphous B with Ni as a sintering aid by reactive hot pressing method. The as-synthesized ceramics exhibited porosity as low as 0.375% and ultra-high Vickers hardness (H_v), as much as 49.808?±?1.683?GPa (for the low load of 0.49?N). It was seen that the addition of Ni greatly improved the sinterability of WB₄ ceramic. Besides, the flexural strength and fracture toughness of WB₄ ceramic were measured for the first time to be 332.857?±?36.763?MPa and 4.136?±?0.259?MPa?m^1/2, respectively, suggesting that the ceramic has good mechanical properties. The effects of sintering temperature and holding time on the densification, Vickers hardness, and mechanical properties of WB₄ ceramics were also investigated systematically as part of our study. The results indicated that increasing the sintering temperature can obviously improve the densification and mechanical properties of the ceramics. The bulk density and Vickers hardness of WB₄ ceramic sintered at 1650?°C for 60?min under 30?MPa revealed the highest values of 6.366?g?cm^?3 and 27.948?±?0.686?GPa (for the high load of 9.8?N), respectively. The flexural strength increased to the highest value of 332.857?±?36.763?MPa for sintering temperature up to 1550?°C, but decreased slightly as the sintering temperature further increased to 1650?°C. On the other hand, the fracture toughness increased gradually with increasing temperature. It was also found that Vickers hardness showed a similar trend as the densification of the samples with increasing temperature and holding time. Besides, no obvious improvements in the densification, mechanical properties, and Vickers hardness of the samples with sintering time were observed in this study. The microstructure and fracture behaviours of the as-synthesized WB₄ ceramic were also revealed, and the toughening mechanism has been discussed.     

Enhanced photodielectric effect in (0.88–x)Bi0.5Na0.5TiO3–0.12BaTiO3 –xBa(Ti0.5Ni0.5)O3–δ (BNBTNO) ceramics

In this work, solid solutions of (0.88–x)Bi_0.5Na_0.5TiO₃–0.12BaTiO₃– xBa(Ti_0.5Ni_0.5)O_3–δ were designed and prepared. These compositions exhibit ferroelectricity at room temperature, with the tetragonal symmetry. The c/a values are varied from ～1.0067 (x?=?0.1) to ～1.0208 (x?=?0.04). A transition from the high–temperature relaxor state to the low–temperature ferroelectric state is demonstrated by the temperature dependence of dielectric data and Raman spectrum. The direct bandgap decreases from 3.40?eV for x?=?0 to 3.16?eV for x?=?0.1. The Ba(Ti_0.5Ni_0.5)O_3–δ addition leads an additional optical absorption peak in the visible range. The obvious photodielectric effect was discovered. In particular, the relative permittivity of the x?=?0.1 composition rises from ～756 to ～807 under light illumination.     

Effect of Ni doping on the structural,electrical, and optical properties of transparent CuCrO2 films grown using pulsed laser deposition

In this study, the structural, electrical, and optical properties of CuCr_1?xNi_xO₂ epitaxial films (x?=?0, 0.01, 0.03, 0.05), which exhibited p-type properties, were investigated. The (001)-oriented epitaxial films were deposited on c-plane α-Al₂O₃ substrates using pulsed laser deposition at a growth temperature of 700?°C and oxygen pressure of 10 mTorr. The optical energy band gap of the CuCr_0.95Ni_0.05O₂ film was determined to be 3.22?eV. The hole carrier concentration of the CuCrO₂ film increased from 5.1?×?10¹⁴ to 2.2?×?10¹⁷ cm^?3 upon doping with 5?at% Ni. Based on Hall measurement and X-ray photoelectron spectroscopy results, it was suggested that the substituted Ni²⁺ dopants at Cr³⁺ sites formed an acceptor level without any charge compensation with Cu²⁺ and/or Cr⁴⁺.