High Curie Point Research Articles

The influence of Calcium doping on structural and electrical properties of ferroelectric Lead Titanate ceramic

A series of Lead Titanate ceramic with various concentration of Calcium has been prepared by solid state reaction method, and some of their physical properties and structural characteristics have been studied. The incorporation of small amount of Calcium results in considerable changes in the dc electrical conductivity and the temperature of the ferroelectric phase transition. Lead Titanate (PT) is a well known ferroelectric with high curie point and low dielectric thus constant making it an attractive proportion for various applications. The synthesis of Calcium modified PbTiO3 was carried using solid state reaction method. Stoichiometric amount of high purity CaO was used as a dopant in different proportion and the final product was in powder form. The X-ray diffraction pattern was taken for pure and CaO modified Lead Titanate. The SEM of the sample was done on JEOL 6360A Analytical Scanning Electron Microscope. There is an observable change in grain size with different molar concentration of Calcium oxide. The DC conductivity of the sample was carried out using two probe method over a range of temperature covering their transition temperature.

Equilibrium phases in the multiferroic BiFeO3-PbTiO3system – a revisit

The(1-x) BiFeO3-(x) PbTiO3 solid solution exhibiting a Morphotropic Phase Boundary (MPB) has attracted considerable attention recently because of its unique features such as multiferroic, high Curie point (T-C similar to 700 degrees C) and giant tetragonality (c/a -1 similar to 0.19). Different research groups have reported different composition range of MPB for this system. In this work we have conclusively proved that the wide composition range of MPB reported in the literature is due to kinetic arrest of the metastable rhombohedral phase and that if sufficient temperature and time is allowed the metastable phase disappears. The genuine MPB was found to be x=0.27 for which the tetragonal and the rhombohedral phases are in thermodynamic equilibrium. In-situ high temperature structural study of x=0.27 revealed the sluggish kinetics associated with the temperature induced structural transformation. Neutron powder diffraction study revealed that themagnetic ordering at room temperature occurs in the rhombohedral phase. The magnetic structure was found to be commensurate G-type antiferromagnetic with magnetic moments parallel to the c-direction (of the hexagonal cell). The present study suggests that the equilibrium properties in this solid solution series should be sought for x=0.27.

Rapid synthesis, structure and photocatalysis of pure bismuth A-site perovskite of Bi(Mg3/8Fe2/8Ti3/8)O3.

Bi(Mg3/8Fe2/8Ti3/8)O3, a member of a small group of pure Bi(3+) A site perovskites, exhibiting a high ferroelectric Curie point (Tc), was rapidly synthesized by a sample method of molten salt synthesis. The purity of Bi(Mg3/8Fe2/8Ti3/8)O3 samples is directly affected by the reaction conditions such as the soaking temperature, and the heating and cooling rates. The as-prepared Bi(Mg3/8Fe2/8Ti3/8)O3 particles are well-formed, cube-shaped single-crystals with sizes ranging from 200-300 nm. The chemical states of Bi and Fe ions are Bi(3+) and Fe(3+) in Bi(Mg3/8Fe2/8Ti3/8)O3. UV-vis diffuse reflectance spectra and preliminary photocatalytic experiments indicate that the pure Bi(3+) A site perovskite of Bi(Mg3/8Fe2/8Ti3/8)O3 has a suitable energy bandgap (1.86 eV) and shows obvious photocatalytic activity for the decolorization of methyl blue under visible-light irradiation. The present work suggests potential future applications of Bi(Mg3/8Fe2/8Ti3/8)O3 in photocatalysis and ferroelectric photovoltaic effects.

Ferroelectricity of Pr2Ti2O7 ceramics with super high Curie point

The perovskite-like layer structured praseodymium titanate (Pr2Ti2O7; PTO) is a good candidate for high temperature piezoelectric application because of its high Curie point. Single phase, dense, textured PTO ceramic was prepared by spark plasma sintering using a two-step method for the first time. The Lotgering orientation factor was 0·87. The Curie point of PTO is >1555±5°C. The dielectric constant increases with grain size due to the decreasing effect of grain boundaries and increasing extrinsic contribution from the ferroelectric domain wall movement. For the first time, PTO was shown to be ferroelectric because it showed piezoelectric activity after poling (d33 = 0·5±0·1 pC N–1).

OS1222 ニオブ酸リチウム双結晶における接合界面の電気的特性

Lattice defects in a ferroelectric material strongly affect its physical properties. However, there are fewer studies on plane and line defects, which are important lattice defects. In the present study, LiNbO_3 bicrystals with domain boundaries are successfully fabricated by diffusion bonding. Here, LiNbO_3 is a widely used ferroelectric material with pyroelectric, piezoelectric, electro-optic and photoelastic properties, and a high Curie point. The resultant boundaries are then investigated using conventional TEM and high-resolution STEM. Moreover, it is found that the boundaries have exhibit specific and interesting physical properties.

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

This work revealed that the solid solution compounds of Sr2−xBaxNb2O7 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 Sr2−xBaxNb2O7 (x < 1.0) was investigated. The solid solution limit of Sr2−xBaxNb2O7 was determined by XRD as x < 0.6. The a‐, b‐, c‐ axes, and cell volume increase with Ba addition. The textured ceramics of Sr2−xBaxNb2O7 were prepared for the first time. The highest d33 was measured as 3.6 ± 0.1 pC/N for Sr1.8Ba0.2Nb2O7.

Effect of synthesized BaTiO3 doping on the dielectric properties of ultra temperature-stable ceramics

The high performance X9R ceramics could be sintered at as low as 1,120 °C by doping 3 mol% synthesized BaTiO3 (SB) additives into the BaTiO3-based ceramics, with a dielectric constant greater than 2,200 at 25 °C and dielectric loss lower than 1.7 %. The effects of SB additives on the microstructure and dielectric properties of BaTiO3-based ceramics were investigated. The dielectric constant of BaTiO3-based ceramics doped with 3 mol% SB was increased due to the promotion of the densification of ceramics. With SB content up to 4.5 mol%, Ti4+’s polarization was depressed, which resulted in the decrease of augmented dielectric constant at 25 °C. The partial solid solution was formed between Pb(Ti, Sn)O3 and BaTiO3, and the substitutions of Pb at A-sites and Sn at B-sites were existed. The strengthen of Ti–O bonds and higher Curie point of Pb(Ti0.55Sn0.45)O3 was helpful to increased the Curie point of the ceramics effectively. Doped with SB additives, the volume of ferroelectric core was increased, and the sharp peak intensity at Curie point was increased accordingly. Capacitance temperature characteristics was improved attributed to the mutual effects of SB and Pb(Ti0.55Sn0.45)O3. The formation of core–shell structure was sensitive to the sintering temperature, so the dielectric properties of ceramics were highly depended on the sintering temperature.

OS1316 強誘電体双結晶を用いた小角粒界の創製とその構造

Lattice defects in a ferroelectric material strongly affect its physical properties. However, there are fewer studies on plane and line defects, which are important lattice defects. In the present study, LiNbO_3 bicrystals with low-angle tilt grain boundaries were successfully fabricated by diffusion bonding. Here, LiNbO_3 is a widely used ferroelectric material with pyroelectric, piezoelectric, electro-optic and photoelastic properties, and a high Curie point. The resultant boundary was then investigated using conventional TEM and high-resolution TEM, and it was found that a boundary dislocation dissociated into two or three partial dislocations with a narrow separation distance. A crystallographic consideration with the TEM observations suggests the Burgers vectors of the partial dislocations and structures of stacking fault.

Sintering and piezoelectric properties of lead-free (K0.38Na0.58Li0.04)(Nb0.86Ta0.10Sb0.04)O3 ceramics doped with Fe2O3

Lead-free (K0.38Na0.58Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (KNLNTS) + x mol% Fe2O3 (x = 0 ∼ 1) ceramics were prepared by conventional solid state reaction technique. The effect of Fe2O3 doping on the phase structure, microstructure and electrical properties of KNLNTS ceramics were studied. The addition of Fe2O3 was found to be effective in enhancing densification of KNLNTS ceramics. When x = 0.3, the piezoelectric constant d33 and planar piezoelectric coupling coefficient kp reached highest while maintaining a relatively high Curie point of 318 °C; d33 = 257 pC/N and kp = 52 %, which suggests that the ceramics are promising for electromechanical transducer and actuator applications.

THE CONTRIBUTION OF ELECTRICAL CONDUCTIVITY, DIELECTRIC PERMITTIVITY AND DOMAIN SWITCHING IN FERROELECTRIC HYSTERESIS LOOPS

Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity, electric conductivity and domain switching in current-electric field curves. At the same time, it is shown how those contributions can affect the shape of the electric displacement — electric field loops (D–E loops). The effects of frequency, temperature and microstructure (point defects, grain size and texture) on the ferroelectric properties of several ferroelectric compositions is reported, including: BaTiO3; lead zirconate titanate (PZT); lead-free Na0.5K0.5NbO3; perovskite-like layer structured A2B2O7with super high Curie point (Tc); Aurivillius phase ferroelectric Bi3.15Nd0.5Ti3O12; and multiferroic Bi0.89La0.05Tb0.06FeO3. This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.

Effect of Sr doping on phase transition and electric behaviour of (Pb0.70Sr0.30)(Zr0.70Ti0.30)O3 ceramics

The ferroelectric (FE) materials are continuously attracting considerable attention due to the interesting combination of their mechanical, electrical and chemical properties and their application in microelectromechanical devices (piezoelectric transformers, motors and transducers). To be more specific, their excellent electrostrictive properties coupled with domain mobility, high Curie point and good stability make these ‘new materials’ important components of electroceramic devices. It is already known that the electrical behaviour of these FE materials largely depends on random elasto-electric fields connected with the diffusion of phase transition and defects distribution. The aim of this article is the exposition of phase transition dependence on Sr2+ homovalent dopant in (Pb0.70Sr0.30)(Zr0.70Ti0.30)O3 ceramics investigated by electrical methods. We demonstrate that electrical examination can be effectively used for drawing decisive applications conclusions from the grain and grain boundary parameters distribution. Modification of FE materials with isovalent ions, but with radii bigger than the original atom, significantly affect its properties, particularly the (Pb,Sr)(Zr,Ti) O3 real part of electrical permittivity shows the change of phase transition from FE to relaxor.

Effect of sintering procedure on the resistivity of (1− x)BaTiO 3− x(Bi 0.5Na 0.5)TiO 3 ceramics

The experimental results on the effect of sintering procedure on the resistivity of high Curie point (1− x)BaTiO 3− x (Bi 0.5Na 0.5)TiO 3 ( x = 0.5, 2, 4, 6, 8, 10, 15, 20 mol%) ceramics, are reported. The sample with x = 0.5 mol% could be semiconducting in air atmosphere sintering, with the Curie point about 149.7 °C. The samples with x ≥ 2 mol% must be sintered at reducing atmosphere. The highest Curie point (about 192 °C) with superior PTC effect could be obtained at the sample with x = 4 mol% when sintered at 1290 °C for 20 min and added 5 g graphite in the crucible for reducing atmosphere. Samples with more BNT contents could not be semiconducting by this sintering procedure. The samples with weak NTC effect could be obtained by firstly air or reducing atmosphere sintering and then different reducing atmosphere treatment. At last, all of the samples with different BNT contents could be semiconducting according to changing sintering atmosphere and procedure.

Piezoelectric Strontium Niobate and Calcium Niobate Ceramics with Super‐High Curie Points

The perovskite‐like layer structured strontium niobate (Sr2Nb2O7) and calcium niobate (Ca2Nb2O7) are good candidates for high‐temperature piezoelectric applications because of their high Curie points. Single‐phase dense Sr2Nb2O7 and Ca2Nb2O7 ceramics with grain‐oriented microstructures were prepared by spark plasma sintering using a two‐step method. The Lotgering orientation factors were 0.86 and 0.70 for Sr2Nb2O7 and Ca2Nb2O7, respectively. The Tc of Sr2Nb2O7 and Ca2Nb2O7 were measured as 1327±5°C and above 1525°C, respectively. The dielectric, piezoelectric, ferroelectric properties, and direct‐current electrical conductivity are higher along the directions perpendicular to the pressing direction compared with parallel. The piezoelectric constant d33 for Sr2Nb2O7 was 2.8±0.2 pC/N.

Textured high Curie point piezoelectric ceramics prepared by spark plasma sintering

The Curie point Tc of ferroelectrics sets the upper temperature limit for their application as piezoelectrics. Some Aurivillius phase and perovskite-like layer structured (PLS) materials are good candidates for high temperature piezoelectric applications because of their high Tc. The Aurivillius phase CaBi2Nb2O9 and PLS Sr2Nb2O7 were densified by ordinary sintering and/or spark plasma sintering (SPS). All of the materials were single phase, and their grains were plate-like. Their density was >95%. The spark plasma sintered ceramics had grain oriented, textured microstructures. The Curie point of CaBi2Nb2O9 was measured as 943±5°C. Ferroelectric switching in CaBi2Nb2O9 was observed at room temperature. The d33 of the textured CaBi2Nb2O9 materials was nearly three times that of ordinary sintered materials. The Curie point of Sr2Nb2O7 was measured as 1327±5°C. Ferroelectric and piezoelectric (2·8 pC N−1) properties were observed for spark plasma sintered textured Sr2Nb2O7 ceramics.

Preparation and modification of high Curie point BaTiO3-based X9R ceramics

BaTiO3 (BT) based X9R ceramics with high permittivity about 1700 were prepared by doping and pre-sintering technique. Pure Bi0.5Na0.5TiO3 (BNT) dopant was synthesized by the conventional solid state reaction first. Using this new approach, high performance BTBNT (BT doped with BNT) materials, owning high Curie temperature (139 °C), flat ferroelectric transition region and large permittivity at room temperature, were obtained. The effects of several dopants on dielectric properties of BTBNT ceramics were measured by the LCR meter. The suppression effect for the peaks in the dielectric constant at Curie temperature of these dopants have been ranked as follows: BiNbO4 > CaZrO3 > Nb2O5 > BNT.

Effect of Pb(Ti, Sn)O3 on the dielectric properties of high dielectric constant X8R BaTiO3-based ceramics

The high dielectric constant X8R dielectric materials could be sintered at 1,240 °C by doping 2.5 mol% Pb(Ti,Sn)O3 additives into the BaTiO3 ceramics, with a dielectric constant greater than 3,400 at 25 °C, dielectric loss lower than 2.0% and temperature coefficient of capacitance (TCC) less than ±15% from −55 to 150 °C, which satisfied X8R specification. The effects of Pb(Ti,Sn)O3 on the microstructure and dielectric properties of BaTiO3-based ceramics were investigated. Doped with Pb(Ti,Sn)O3 additives, the partial solid solution was formed between Pb(Ti,Sn)O3 and BaTiO3. Due to the high Curie point of Pb(Ti,Sn)O3, the Curie point of the ceramics was markedly shifted to higher temperature about 150 °C, and the temperature coefficient of capacitance curves was flattened. The increase of the tetragonality (c/a ratio) and the fine microstructure were resulted in the increase of dielectric constant. With Pb(Ti, Sn)O3 content up to 3 mol%, the depression of Ti4+’s polarization and the decrease of the tetragonality (c/a ratio) were resulted in the decrease of dielectric constant.

Piezoelectric and Ferroelectric Properties of Bismuth Tungstate Ceramics Fabricated by Spark Plasma Sintering

Single‐phase bismuth tungstate (Bi2WO6) ceramics with high relative density (>99%) were fabricated by spark plasma sintering. Ferroelectric, dielectric, and piezoelectric properties of Bi2WO6 ceramics were investigated. Almost saturated polarization–electric field (P–E) hysteresis loops with a remanent polarization (Pr) of ∼16.1 μC/cm2 and a coercive field (Ec) of ∼3.7 kV/mm were obtained. Curie point and second phase transition temperatures were observed at 937°±5° and 665°±5°C, respectively. The average piezoelectric constant (d33) of this high Curie point ceramic is 15±0.2 pCN−1.

Temperature Dependence of Magnetization of Lu<sub>2</sub>Fe<sub>17</sub> Compound in Different Structural States

In the present work we report our studies of temperature dependence of magnetization and structure analysis of Lu2Fe17 samples. The samples revealed various, coarse grained, submicrocrystalline, and nanocrystalline microstructures. It was found that in nanocrystalline state the Lu2Fe17 compound has a higher coercive force, retains phase composition and does not disintegrate during heating. The curves of the temperature dependence of magnetization were recorded for all investigated structural states and indicated that nanocrysatlline sample had a higher Curie point.

In situ investigation of thermally influenced phase transformations in (pb0.92sr0.08) (zr0.65ti0.35)o3 thin films using micro-raman spectroscopy and x-ray diffraction

Thin films of ferroelectric strontium-doped lead zirconate titanate [PSZT, (Pb(0.92)Sr(0.08))(Zr(0.65)Ti(0.35))O(3)] deposited by RF magnetron sputtering have been analyzed by in situ analysis techniques. The in situ techniques employed for this study include micro-Raman spectroscopy and X-ray diffraction (XRD), and variations in thin film structure and orientations for temperatures up to 350 degrees C and 750 degrees C for the respective techniques have been studied. The samples analyzed were PSZT thin films deposited on platinum-coated silicon substrates at either room temperature or at 750 degrees C. In situ measurements using micro-Raman spectroscopy and XRD techniques have been used to identify the Curie point for poly-crystalline PSZT thin films and to determine the temperature-activating significant grain growth for room-temperature-deposited PSZT thin films. To study the presence of hysteresis, analysis was carried out during both temperature ramp-up and ramp-down cycles. Raman measurements showed expected bands (albeit weak), and the in situ measurements have detected variations in the crystal structure of the thin film samples, with negligible variations between the heating and cooling cycles. A combination of the Raman and XRD results has shown that the temperature-activating significant grain growth for the room-temperature-deposited films is about 275 degrees C and the Curie point lies between 325 and 400 degrees C. This relatively high Curie point makes these films suitable for wide temperature range applications.

Effect of A Site Substitution on the Properties of CaBi2Nb2O9 Ferroelectric Ceramics

The effect of A‐site substitution on the piezoelectric coefficient, high‐temperature dc resistivity, and thermal depoling behavior of Aurivillius phase CaBi2Nb2O9 ferroelectric ceramics was investigated. Ceramics with the general formula of Ca1−xMxBi2Nb2O9, where M=Na, (Na,Ce), (Na,La), and La, were prepared by conventional solid‐state sintering. All the ceramics were single‐phase ferroelectrics with high Curie points (∼900°C). The doped ceramics, Ca0.9Na0.1Bi2Nb2O9, Ca0.9(NaLa)0.1Bi2Nb2O9, Ca0.95La0.05Bi2Nb2O9, and Ca0.9La0.1Bi2Nb2O9, had improved resistance to thermal depoling compared with Ca2Bi2Nb2O9 and were stable up to 800°C. The donor dopants increased the dc electrical resistivity, while the acceptor dopants decreased it. The donor‐doped Ca0.95La0.05Bi2Nb2O9 had a higher piezoelectric constant (d33=12.8 pC/N) compared with CaBi2Nb2O9 (d33=5.8 pC/N), and its electrical resistivity was higher than 106Ω·cm at 600°C. These properties suggest that doped CaBi2Nb2O9 ceramics might be good candidates for high‐temperature piezoelectric applications.