Dielectric and Pyroelectric Properties of （Pb0.50Sr0.50）TiO3 Ceramics

Lead strontium titanate （Pb0.50Sr0.50）TiO3 （PST） ceramics are prepared by the traditional ceramic processing. The dielectric constants and dielectric loss have been investigated in a temperature range from 25℃ to 300℃. The maximum dielectric constants for unpoled and poled samples are 9924 and 9683, respectively. The temperatures of phase transition for unpoled and poled samples are observed at 153℃ and 157℃, respectively. The phasetransition temperatures for unpoled and poled samples are not equal, which results from the polarization state of the domains. The remnant polarization and the coercive electric field are 18 uC/cm^2 and 6 kV/cm, respectively, from polarization-electric field （P - E） hysteresis loop. The temperature dependence of pyroelectric coefficients of the PST ceramics is measured by a dynamic technique. The dielectric constant and loss Lan δ of the poled PST ceramics are 813 and 0.010, respectively. The pyroelectric coefficients and figure of merit are 294 uC/cm^2 K and 13.6 × 10^-6 pa^-0.5, respectively, at room temperature 25℃and frequency lOOHz.     

The low-temperature sintering and microwave dielectric properties of （Zno.7Mgo.3） TiO3 ceramics with H3BO3

The effects of the addition of H3BO3 on the microstructure, phase formation, and microwave dielectric properties of （Zn0.TMg0.3）TiO3 ceramics sintered at temperatures ranging from 890 ℃ to 950 ℃ are investigated. H3BO3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 ℃due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H3BO3. With the increase in H3BO3 content, the dielectric constant （er） monotonically increases, but the quality factor （Q x f） reaches a maximum at 1 wt% H3BO3, and the apparent density of ZMT ceramics with H3BO3〉 1 wt% gradually decreases. At 950 ℃, the ZMT ceramics with 1% H3BO3 exhibit excellent microwave dielectric properties： er = 19.8, and Q x f -- 43800 GHz （8.94 GHz）.     

Effects of （LiCe） co-substitution on the structural and electrical properties of CaBi2Nb209 ceramics

The piezoelectric,dielectric,and ferroelectric properties of the(LiCe) co-substituted calcium bismuth niobate(CaBi2Nb2O9,CBNO) are investigated.The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tan δ decreased.This makes poling using(LiCe) co-substitution easier.The ceramics(where represents A-site Ca2+ vacancies,possess a pure layered structure phase and no other phases can be found.The Ca0.88(LiCe)0.04 0.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties,with piezoelectric coefficient(d 33) and Curie temperature(TC) found to be 13.3 pC/N and 960 C,respectively.The dielectric and piezoelectric properties of the(LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours.This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.     

Improved multiferroic properties of La-doped 0.6BiFeO3—0.4SrTiO3 solid solution ceramics

The 0.6（Bi1-xLax）FeO 3-0.4SrTiO 3（x = 0,0.1） multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO3 and La in BiFeO3.The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure.The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO3 and substitution of La.The values of the dielectric constant ε r and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature.The La-doped 0.6BiFeO3-0.4SrTiO3 ceramics exhibit improved dielectric and ferroelectric properties,with higher dielectric constant enhanced remnant polarization（Pr） and lower leakage current at room temperature.Compared with a anti-ferromagnetic BiFeO3 compound,the 0.6（Bi0.9La0.1）FeO3-0.4SrTiO3 sample shows the optimal ferromagnetism with remnant magnetization M r ～ 0.135 emμ/g and ferroelectricity with Pr ～ 5.94 μC/cm 2 at room temperature.     

Effects of BaCu（B2Os） addition on sintering temperature and microwave dielectric properties of BasNb4O15-BaWO4 ceramics

The effects of BaCu（B2Os） （BCB） addition on the microstructure, phase formation, and microwave dielectric proper- ties of BasNb4015-BaWO4 ceramic are investigated. As a sintering aid, BaCu（B2Os） ceramic could effectively lower the sintering temperature of BasNb4015-BaWO4 ceramic from 1100 ℃ to 950 ℃ due to the liquid-phase effect. Meanwhile, BaCu（B2Os） addition effectively improves the densification of BasNb4015-BaWO4 ceramic and significantly influences the microwave dielectric properties. X-ray diffraction analysis reveals that BasNb4015 and BaWO4 coexist with no crystal phase of BaCu（B2Os） in the sintered ceramics. The BasNb4015-BaWO4 ceramics with 1.0 wt% BaCu（B2Os） sintered at 950 ℃ for 2 h presents good microwave dielectric properties of er = 19.0, high Q× f of 33802 GHz and low vf of 2.5 ppm/℃.     

Dimension effects on the dielectric properties of fine BaTi03 ceramics

It is found that the core-shell structured grains are easy to produce for fine grain doped BaTiO3 ceramics in the sintering process. We study the influence of the core-shell structure on the Curie-Weiss temperature and dielectric properties of BaTiO3 ceramics by using effective medium approximation （EMA）. Considering the second approximation, the dielectric properties of fine grain doped BaTiO3 ceramics are consistent with experimental data.     

Thermal Stability and Humidity Resistance of ScTaO4 Modified （K0.5Na0.5）NbO3 Ceramics

Lead-free （Na0.5K0.5）NbO3-xmol% ScTaO4 （x=0-1.5） ceramics are prepared using the conventional solid-state reaction method and their properties are investigated in detail. The results indicate that the piezoelectric properties and density are improved by the introduction of ScTaO4. Due to the high orthorhombic-tetragonal phase transition temperature TO-T （around 200°C）, stable piezoelectric properties against temperature are obtained. In a wide temperature range of 15-160°C, kp of the （Na0.5K0.5）NbO3-0.5mol% ScTaO4 ceramic remains almost unchanged and d31 increases slightly from 59pC/N to 71pC/N. The deliquescent problem is effectively solved by the addition of ScTaO4. The piezoelectric properties of ScTaO4 modified （Na0.5K0.5）NbO3 ceramics show no obvious reduction and dielectric loss increases slightly after 120h of immersion. From the analysis, it is suggested that the density is an important factor that improves the humidity resistance of the specimens.     

Properties of Co-Doped 0.92（Na0.5Bi0.5） TiO3-0.08BaTiO3 Lead-Free Ceramics

Lead-free piezoelectric ceramics 0.92（Bi0.5Na0.5）TiO3-0.08BaTiO3 ＋ xmol% Co3＋ （BNBT-Co, x = 0-8） are prepared by the solid state reaction method. Effects of the amount of Co^3＋ on the electrical properties and phase transition are studied. The results indicate that the addition of Co^3＋ enhances the mechanical quality factor Q^3＋ significantly, whereas the dissipation factor tanδ has a minimum value at x = 3.5. Meanwhile, addition of Co^3＋ leads to small decreases of piezoelectric constant d33, and planar electromechanical coupling kp. The present 0.92（Bio.aNao.5） TiO3-0.08BaTiO3＋3.5 moi% Co^3＋ ceramics exhibit good performance with mechanical quality factor Qm = 910, piezoelectric constant d33 = 106pC/N, planar electromechanical coupling kp =10% and dissipation factor tanδ = 1.1% at 1 kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Td and Tm appear in the curves of ε33^T vs temperature for the pure BNBT ceramics. However, the first dielectric peak Td disappears after the addition of Co^3＋, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.     

Effects of Li Substitution and Sintering Temperature on Properties of Bi0.5（Na,K）0.5TiO3 Lead-Free Piezoelectric Ceramics

Bi0.5 （Na0.72K0.28- x Lix ）0.5 TiO3 （BNKLT- 100x） lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d33 Of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130℃, the d33 value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100℃ has the highest piezoelectric constant d33 of 252pC/N, with the electromechanical coupling factors kp of 0.32 and kt of 0.44.     

KNN Based Lead-Free Piezoceramics with Improved Thermal Stability

Lead-free piezoelectric ceramics （1 - x） （Na0.53K0.404 Li0.066）Nb0.92 Sb0.08 03 ＋xZrTiO3 are fabricated by conventional solid-state sintering method, and their dielectric and piezoelectric characteristics are investigated. With the addition of SrTiO3, the growth of the grain size is restrained, meanwhile the phase transition temperature of orthorhombic-tetragonal is shifted below room temperature. It is found that the ceramics with x = 0.010 exhibit excellent piezoelectric properties （d33 = 220 pC/N, kp = 41%, kt = 39%） and improved thermal stability around room temperature. The results indicate that these materials are promising lead-free piezoceramics for practical operations.     

Electrical Properties of La-Doped Al2O3 Films on Si （100） Substrates as a High-Dielectric-Constant Gate Material

Amorphous La-doped Al2O3 （La： Al2O3） thin films are deposited on n-type （100） Si substrates by rf magnetron co-sputterlng. The composition of the deposited films is measured by energy dispersive x-ray spectroscopy： Capacitance-voltage measurement shows that the dielectric constant k of La-doped Al2O3 films ranges from 8.5 to 11.6 with the increasing La content, and the highest k value of 11.6 is obtained for the 20.14% La content film. In the structure of the Al/La：Al2O3/Si metal oxide semiconductor, the dominant conduction stems from the space- charge-limited current at different temperatures. In addition, the wavelength dependence of the transmittance is studied by ultraviolet spectroscopy and the band gap of all the deposited films is above 5.5eV. The results demonstrate that La-doped Al2O3 can meet the requirement of next-generation gate materials.     

Dielectric Properties of Fine-Grained BaTiO3 Ceramics under High Pressure

We investigate the temperature dependence of the dielectric constant of BaTiO3 ceramic with coarse to nanograin size under different hydrostatic high pressures up to 5000 bar in the range between room temperature and 200℃. The ferroelectric-to-paraelectric phase transition temperatures Tc are determined from the peak of dielectric constant versus temperature. The values of average grain-size are estimated from the SEM images. It is found that the magnitude of dTc/dp varies considerably from sample to sample depending on grain size. The Curie point Tc of the sample with small grain size decreases more sharply than that of samples with larger one.     

Superconducting Transition Temperature and Metal--Semiconductor Transition Temperature in YBa2Cu4O8/La0.67Ca0.33MnO3/YBa2Cu4O8 Trilayer Films

YBa₂Cu₄O₈/La_0.67Ca_0.33MnO₃/YBa₂Cu₄O₈(YBCO/LCMO/YBCO) trilayer films were prepared by magnetron facing-target sputtering. For the first time, the oscillatory behaviour of superconducting transition temperature T_c,ON with the thickness of LCMO (d_L) has been observed. The strongest nonmonotonic information in the T_c,ON--d_L curves appears clearly when d_L is larger than the critical thickness d_L^CR. The metal--semiconductor transition temperature can only be detected at d_L>d_L^CR. The dependence on the ferromagnetic spacer layer in YBCO/LCMO/YBCO systems suggests strongly the interplay of ferromagnetic and superconducting couplings.     

Structural and Optical Properties of Nanocrystal In2O3 Films by Thermal Oxidation of In2S3 Films

In₂S₃ nanocrystalline films are prepared on glass substrates by the spray pyrolysis technique using indium chloride and thiourea as precursors. The deposition is carried out at 350°C on glass substrates. The films are then annealed for two hour at 200, 400, 600, and 800°C in O₂ flow. This process allows the transformation of nanocrystal In₂O₃ films from In₂S₃ films and the reaction completes at 600°C. These results indicate that the In₂O₃ film prepared by this simple thermal oxidation method is a promising candidate for electro-optical and photovoltaic devices.     

Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing

Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380℃. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048 MPa. Its bending strength and compressive strength are 529 MPa and 1466 MPa, respectively.     

Microstructure-dependent giant dielectric response in CaCu3Ti4O12 ceramics

CaCu₃Ti₄O₁₂ ceramics were prepared at the sintering temperatures ranged from 1025 to 1125 °C, and the dielectric characteristics were evaluated together with the microstructures. The giant dielectric constant with the maximum of 53,120 was obtained in CaCu₃Ti₄O₁₂ ceramics at room temperature and 10 kHz, and strong processing and microstructure dependence of dielectric characteristics of the present ceramics was determined. The precipitation of the dispersed Cu-rich secondary phases of CuO and/or Cu₂O and their network structure provided the extrinsic origins of the enhanced giant dielectric response, and the present findings would offer the greater potential for enhancing the giant dielectric constant and controlling the dielectric loss in CaCu₃Ti₄O₁₂ ceramics by optimizing the microstructures.     

Effect of Cu-stoichiometry on the dielectric and electric properties in CaCu3Ti4O12 ceramics

CaCu_3+yTi₄O₁₂ (y=0, ±0.025, ±0.05, ±0.1 and −0.15) ceramics are prepared by the conventional solid-state reaction technique under sintering condition of 1050 ^°C, 10 h. X-ray diffraction shows that they all have the good crystalline structure. Cu-deficient ceramics exhibit the microstructures of uniform grain size distribution, whereas both Cu-stoichiometric and Cu-rich ceramics display microstructures of bimodal grain size distribution. The largeness of low-frequency dielectric permittivity at room temperature is found to be very sensitive to the Cu-stoichiometry. Upon raising the measuring temperature, all of the ceramics present commonly three semicircles in the complex impedance plane. It indicates that there exist three distinct contributions, which are ascribed to arising from domains, grain boundaries and domain boundaries. In addition, the influence of CuO segregation on the dielectric and electrical properties is also discussed.     

Improvement in Dielectric Tunability of Ba0.6Sr0.4TiO4-Mg2TiO4 Composite Ceramics via Heterogeneous Nucleation Processing

Dielectric tunable composite ceramics Ba0.6Sr0.4 TiO4-Mg2 TiO4 （BST-MT） are prepared with a heterogeneous nucleation sol-gel approach. The Mg2 TiO4 powders are synthesized by the conventionM solid-state reaction method. The micro-sized MT powders with dispersant Ciba-4010 are introduced into Ba-Sr-Ti sol to obtain uniform and homogeneous mixture compounds with nano-sized BST particles synthesized via heterogeneous nucleation （HN） in the sol-gel process. Thus, the mierostructural and dielectric properties can be tailored. The dielectric constants of BST-MT composite ceramics can be adjusted in a larg＇e range from 294 to 1790, and the dielectric tunability can be adjusted from 29.4% to 37.0% with different MT contents from 60wt% to 20wt%. Compared to the samples prepared by the conventional solid-state （SS） process, the BST-MT composite ceramics by the heterogeneous nucleation sol-gel process exhibit a more uniform microstructure, and improve dielectric properties.     

Photoemission Spectroscopy and Electronic Structures of LiMn2O4

We study the electronic structures of LiMn2O4 by x-ray and ultraviolet photoelectron spectroscopy （XPS, UPS） and resonant photoelectron spectroscopy （RPES）. XPS data suggest that the average oxidation state of Mn ions is 3.55, probably due to the small amount of lithium oxides on the surface. UPS and RPES data imply that Mn ions are in a high spin state, and RPES results show strong Mn3d-O2p hybridization in the LiMn2O4 valence band.     

Structural Transition of Gd2O3：Eu Induced by High Pressure

The structural transition of bulk and uano-size Gd2O3：Eu are studied by high pressure energy disperse x-ray diffraction （XRD） and high pressure photoluminescence. Our results show that in spite of different size of Gd2O3 particles, the cubic structure turns into a possible hexagonal one above 13.4 GPa. When the pressure is released, the sample reverses to the monoclinic structure. No cubic structure presents in the released samples. That is to say, the compression and relaxation of the sample leads to the cubic Gd2O3：Eu then turns into the monoclinic one.