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Ta-doped Ti1-xTaxCoSb (0≤x≤0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900 K. The Ti1-xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1-xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900 K. This value is about ten times larger than that of the undoped TiCoSb compound. [ABSTRACT FROM AUTHOR]

Single phases of SrBi2-χNdχNb2O9 (χ=0, 0.1, 0.2, and 0.4) ceramics were prepared by the solid-state reaction method and studied by dielectric and Raman spectroscopy. The substitution of Nd3+ for Bi3+ induced a dielectric relaxation behavior for SrBi2-χNdχNb2O9 (χ=0.1, 0.2, and 0.4). When χ=0.4, the dielectric response of SrBi1.6Nd0.4Nb2O9 is characteristic of typical relaxor ferroelectrics, which could be attributed to the disorder induced by the Nd3+ substituting for Bi3+ in Bi2O2 layers. The dielectric relaxation of SrBi1.6Nd0.4Nb2O9 was fitted using the Vögel-Fulcher relationship, which indicates that SrBi1.6Nd0.4Nb2O9 is analogous to a spin glass with thermally activated polarization fluctuations above a static freezing temperature. Raman spectra of SrBi2-χNdχNb2O9 ceramics could indicate that the structural distortion of NbO6 octahedron decreases with the increase in Nd content, which results in the decrease in Tm for SrBi2-χNdχNb2O9 ceramics. [ABSTRACT FROM AUTHOR]

The complex dielectric permittivity of the morphotropic phase boundary [001]-oriented PMN–x%PT single crystal with x=33%, grown by the modified Bridgman technique, has been investigated as a function of both temperature and dc poling field. Structural phase transformation sequence is discussed in the light of polarization rotation process. A remarkable shift in the rhombohedral-tetragonal phase transition temperature is observed with changing of the poling field. It is found that high temperature poled state remained stable even after removal of the field. [ABSTRACT FROM AUTHOR]

Studies the control of the B-site order of lead Pb(Mg[sub 1/3]Nb[sub 2/3)O[sub 3] by the partial substitution at the A site by both donor La[sup 3+]/Bi[sup 3+] and acceptor K[sup +1]. Origins of Raman bands; B-site order induced by A-site substitution.

Abstract: Zr4+ doped multiferroic ceramics samples BiFe1−x Zr x O3 (x=0, 0.02, 0.04, 0.06, 0.08, 0.10) were prepared by a solid state reaction method and characterized by X-ray diffraction and X-ray Absorption Fine Structure analysis. X-ray diffraction analysis showed that the characteristic peaks of samples were shifted toward a lower angle with the increase of Zr4+ doping concentration. It indicated that the doped Zr4+ ions entered into the crystal lattice. The length of Zr3O bond was calculated based on the results of X-ray Absorption Fine Structure analysis. The abnormal dielectric constant near the Neel temperature of BiFe1−x Zr x O3 indirectly demonstrated the coupling between magnetic and electric properties of BiFe1−x Zr x O3. The Neel temperature of Zr4+ doped BiFeO3 was ∼20°C lower than that of the undoped BiFeO3. The Neel temperature of BiFe1−x Zr x O3 will be different if the doping amount of Zr4+ is different. However, all the prepared samples are antiferromagnetic. [Copyright &y& Elsevier]

Abstract: SrBi2−x La x Nb2O9 (x =0, 0.05, 0.1, 0.2 and 0.35) ceramics were prepared by a conventional solid-state reaction method. Their structure and dielectric properties were investigated. X-ray diffraction analysis showed that single-phase layered perovskites were obtained. A relaxor like transition was observed in SrBi2−x La x Nb2O9 with x =0.2 and 0.35. For the specimens with x =0.05 and 0.1, a relaxation-type dielectric loss peak was observed in the temperature range of 30–150°C. The temperature of the maximum dielectric constant T m decreases linearly with increasing La content. The degree of frequency dispersion ΔT m , which is the T m difference between 10kHz and 1MHz, increases from 0°C for x =0–7°C for x =0.35. However, when x =0.1, ΔT m equals −1°C, which might be attributed to oxygen-vacancy-induced dielectric relaxation. In addition, La substitution results in a decrease in both remanent polarization and coercive field. [Copyright &y& Elsevier]

Sr1− xCa xBi2Nb2O9 ( x=0, 0.2, 0.4, 0.6, 0.8 and 1) ceramics were prepared by a conventional solid-state reaction method. Their dielectric and structural properties were investigated. X-ray diffraction analysis indicated that single-phase layered perovskites were obtained. For Ca-substituted specimens, a dielectric relaxation peak is observed in the temperature range of 30°–150°C, and there is a broader para-ferroelectric phase transition peak. The temperature of the maximum dielectric constant Tm increases linearly with increasing Ca content. Raman spectra indicate that a small amount of Ca2+ is incorporated into Bi sites in the Bi2O2 layers, and an increase in the degree of distortion of NbO6 octahedra for Ca-substituted specimens should be one of the reasons for the increase in Tm compared with SrBi2Nb2O9. [ABSTRACT FROM AUTHOR]

Abstract: For (1− x)Pb(Mg1/3Nb2/3)O3-xPbTiO3, composition dependence of dielectric tunability under the dc bias field and dielectric hysteresis during the circle of external electric field were studied. The highest dielectric tunability of 71% (at the dc bias of 1000V/mm) and the lowest dielectric hysteresis were observed in the 0.9PMN-0.1PT sample. The effect of circled electric field on the dielectric hysteresis was more remarkable than that on the dielectric aging. Moreover, the effect of the filed-cooled process on the ferroelectric properties was also investigated. In the polycrystalline 0.7PMN-0.3PT sample cooled under a strong dc electric field, a remarkable imprint effect was reported. The preferred direction induced by a strong external electric field was partially reserved after removing the electric field. This imprint effect and the dielectric hysteresis have been tentatively interpreted by reorientation and alignment of polar vectors. [Copyright &y& Elsevier]

SrBi2− xNd xNb2O9 ( x=0, 0.05, 0.2, 0.35) ceramics were synthesized by the traditional solid-state sintering method. X-ray diffraction analysis showed that single-phase-layered perovskites were obtained for all compositions. The substitution of Nd3+ for Bi3+ induced a relaxor behavior of frequency dispersion for Nd-doped SrBi2Nb2O9.The parameter of frequency dispersion Δ Tm, which is the Tm between 1 kHz and 1 MHz, increases from 0°C for x=0 to 13°C for x=0.35, and the degree of relaxor behavior γ increases from 0.96 for x=0 to 2.02 for x=0.35. The temperature of the maximum dielectric constant Tm decreases linearly with an increase in the Nd content ( x). [ABSTRACT FROM AUTHOR]

Abstract: SrBi2(Nb1−χ Ta χ )2O9 (0≤ χ ≤1.0) bismuth layered structured ferroelectric (BLSF) ceramics were prepared by the conventional solid-state reaction sintering method. XRD analysis indicated that a single phase of SrBi2(Nb1−χ Ta χ )2O9 was formed for all compositions. The substitution of Ta for Nb decreases Curie temperature (T c), maximum permittivity (ɛ m), remnant polarization (P r) and coercive field (E c), whereas temperature coefficient of resonance frequency (TCF) increases with the increase in Ta content for SrBi2(Nb1−χ Ta χ )2O9. All of compositions have a low permittivity (ɛ r), a low electromechamical coupling coefficient (K p) and a high mechanical quality factor (Q m), which are advantageous to be used in piezoelectric resonator device. [Copyright &y& Elsevier]