Wenbin Su

Influences of ScTa co-substitution on the properties of Ultra-high temperature Bi3TiNbO9-based piezoelectric ceramics

The effect of (Sc,Ta) doping on the properties of Bi3TiNbO9-based ceramics was investigated. The (Sc,Ta) modification greatly improves the piezoelectric activity of Bi3TiNbO9-based ceramics and significantly decreases the dielectric dissipation. The d33 of Bi3(Ti0.96Sc0.02Ta0.02)NbO9 was found to be 12 pC/N, the highest value among the Bi3TiNbO9-based ceramics and almost 2 times as much as the reported d33 values of the pure BTNO ceramics (~6pC/N). The high TC (higher than 900xa0°C) and stable piezoelectric and dielectric properties, demonstrating that the (Sc,Ta) modified Bi3Ti1−xScx/2Tax/2NbO9-based material a candidate for ultrahigh temperature applications. The new (ScTa) modification has an important typical significance, the way should be used for reference in constructing the new high performance materials.

Enhanced piezoelectricity in plastically deformed nearly amorphous Bi12TiO20-BaTiO3 nanocomposites

Bulk Bi12TiO20-BaTiO3 (BTO-BT) nanocomposites are fabricated through the high-temperature interfacial reaction between nanometer-sized BaTiO3 particles and melting Bi12TiO20. Although the obtained BTO-BT nanocomposites are nearly amorphous and display very weak ferroelectricity, they exhibit relatively strong piezoelectricity without undergoing the electrical poling process. The volume fraction of crystalline Bi12TiO20 is reduced to less than 10%, and the piezoelectric constant d33 is enhanced to 13 pC/N. Only the presence of the macroscopic polar amorphous phases can explain this unusual thermal stable piezoelectricity. Combining the results from X-ray diffraction, Raman spectroscopy, and thermal annealing, it can be confirmed that the formation of macroscopic polar amorphous phases is closely related to the inhomogeneous plastic deformation of the amorphous Bi12TiO20 during the sintering process. These results highlight the key role of plastically deformed amorphous Bi12TiO20 in the Bi12TiO20-based pola...

Enhanced Thermoelectric Response of Ca0.96Dy0.02Re0.02MnO3 Ceramics (Re = La, Nd, Sm) at High Temperature

Perovskite-type Ca0.98Dy0.02MnO3, Ca0.96Dy0.04MnO3, and Ca0.96Dy0.02 Re0.02MnO3 (Rexa0=xa0La, Nd, Sm) were prepared by solid-state reaction, and their thermoelectric properties were evaluated between 300 and 1000xa0K. All were single-phase, with an orthorhombic structure, and had metal-like temperature dependence of resistivity and Seebeck coefficient. The second doping element, Rexa0=xa0La, Nd, or Sm, introduced a larger carrier concentration, leading to a decrease in both resistivity and Seebeck coefficient. This contributed to lower thermal conductivity by introducing a second element into the system. The highest figure of merit, 0.20, was obtained for Rexa0=xa0La at 973xa0K; this was an increase of almost 100% compared with Ca0.98Dy0.02MnO3 at the same temperature.

Accurate measurement of Seebeck coefficient.

In this work, it was investigated how to measure Seebeck coefficient accurately. The offset voltages, between the specimen and measurement wires, might influence the results measured significantly and should be eliminated during measuring process. They do not depend on temperature difference but on temperature and include two parts: the intrinsic component related to the materials and the random one related to the contact. The inversion method could eliminate the offset voltages more accurately than the traditional differential methods, and thus measure Seebeck coefficient more accurately. The accuracy of Seebeck coefficient measurement could be further improved by performing a proper temperature difference, optimizing temperature control, and using an electromagnetic screen. The most accurate results were obtained with a standard deviation of 0.06 μV/K, measured under temperature difference of 1 K, temperature variation of 0.002 K, and with an iron electromagnetic screen.

The phase structure and electrical performance of the limited solid solution CuFeO2–CuAlO2 thermoelectric ceramics

The limited solid solutions of nominal (1u2009−u2009x) CuFeO2u2009−u2009xCuAlO2 have been prepared by conventional solid-state reaction, and thermoelectric property has been measured. From the XRD powder pattern, we found that the major phase of the limited solid solution is rhombohedral delafossite structure when the composition is near the end members. Cubic Cu(Fe,Al)2O4 phase has been formed in composition from xu2009=u20090.4 to 0.8. Electrical resistivity of samples with major delafossite structure is lower than that of samples with Cu(Fe,Al)2O4 phase. In the zone of phase transform, the electrical resistivity can be got with lower value, such as xu2009=u20090.2, 0.3 and 0.9. The Seebeck coefficient for the limited solid solution with delafossite structure is positive in whole measured temperature range from 300 to 923xa0K. In the end, the power factor for the limited solid solution with major delafossite structure shows higher value, which is resulted from the lower electrical resistivity by the phase transposition. The highest power factor of 1.14u2009×u200910−4xa0W/mK2 has been addressed at 907xa0K for xu2009=u20090.2, which value is enhanced by 3–4 times than that of pure phase CuFeO2 or CuAlO2.

Piezoelectricity and excellent temperature stability in nonferroelectric Bi12TiO20–CaTiO3 polar composite ceramics

Nonferroelectric Bi12TiO20–CaTiO3 (BT–CT) composite ceramics were prepared through an interfacial reaction between presynthesized crystalline CaTiO3 and crystalline Bi12TiO20 phases at various sintering temperatures. After sintering at temperatures above the melting point of Bi12TiO20, both direct and converse piezoelectric effects were observed in these composites for the first time. Because neither CaTiO3 nor Bi12TiO20 is ferroelectric and because no obvious crystallographic orientation was found in these sintered composites, the temperature gradient-driven plastic flexoelectricity of the grain boundary amorphous phases might be the main poling mechanism. In this work, the highest d33 value of 8 pC N−1 was obtained in the samples sintered at 860 °C, which were found to contain a large amount of amorphous Bi12TiO20 and to possess the lowest density. For these BT–CT polar composite ceramics, the piezoelectric activity, the dielectric loss (tgu2006δ ≈ 0.1%), the mechanical quality factor (Qm ≈ 2300), the depoling temperature (Td ≈ 880 °C) and the temperature stability of the resonance frequency are all comparable to those of the well-known bismuth layer-structured ferroelectrics, which indicates that these new polar composite ceramics are promising candidates for high-temperature piezoelectric applications.

Effects of sintering atmospheres on thermoelectric properties, phase, microstructure and lattice parameters c/a ratio of Al, Ga dual doped ZnO ceramics sintered at high temperature

Thermoelectric properties, phase and microstructural investigation of (Zn1−x−yAlxGay)O, where xu2009=u20090.02, yu2009=u20090.04, 0.05 and xu2009=u20090.03, yu2009=u20090.01, 0.02 are studied at a high temperature of 1450xa0°C in this article. We have focused on the effects of sintering atmospheres on thermoelectric properties, phase, and microstructure in the air as well in the argon atmosphere. The Seebeck coefficient (S) and electrical resistivities (ρ) measured in air and argon atmospheres have an evidential large difference. The air sintered Al, Ga co-doped ZnO has higher power factor (S2σ) of the order 720.9xa0µWxa0K−u20092xa0m−u20091 and lower electrical resistivity (ρ) of 5.803xa0mΩxa0cm for the nominal formula (Zn1−u2009x−yAlxGay)O, with xu2009=u20090.03, yu2009=u20090.01 as compared to the power factor 543.6xa0µWxa0K−u20092xa0m−u20091 and electrical resistivity of the order 1.550xa0mΩxa0cm at 692.2xa0°C sintered in the argon atmosphere at the same temperature i.e. 1450xa0°C. The power factor of the air sintered sample with xu2009=u20090.03, yu2009=u20090.01 is 1.4 times higher than the argon sintered sample with the same composition. The difference in power factors and electrical resistivities are linked to sintering atmospheres. We will investigate the effects of sintering atmospheres of the co-doped ZnO and will study thermoelectric properties, phase, and microstructures of the co-doped ZnO.

Effects of potassium interstitial doping on thermoelectric properties of Sr 0.7 Ba 0.3 Nb 2 O 6−δ ceramics

The thermoelectric properties of potassium interstitial doped Sr0.7Ba0.3KxNb2O6−δ ceramics were investigated in the temperature range from 323 to 1073xa0K. The thermoelectric power factor is improved enormously due to the potassium interstitial doping combined with a reductive calcination method. The potassium dopants not only act as carrier donors but also modulate the electronic structures. Thus, the electrical conductivity increases remarkably, and the Seebeck coefficient, meanwhile, maintains considerable values at high temperatures. Only the moderate doping content xu2009=u20090.10 contributes to reducing the lattice thermal conductivity. Thus, the sample Sr0.7Ba0.3K0.1Nb2O6−δ shows the highest ZT value of 0.23 at 1073xa0K.

Thermoelectric Properties, Phase Analysis, Microstructure Investigation and Lattice Parameters c/a Ratio of Al 3+ and In 3+ Substituted ZnO Sintered at High Temperature under Argon Atmosphere

Al2O3 and In2O3 co-doped Zinc oxide (ZnO) system have been studied for enhancing thermoelectric properties of ZnO. Al2O3 and In2O3 are doped with ZnO via solid-state solution method. The compositions were sintered at 1400°C in Argon atmosphere. The thermal and electrical properties of the system are investigated. The power factor of the order 481.8 μWK-2m-1 at 692.3°C and Seebeck coefficient of the order -133.99 μVK-1 at 691.4°C was obtained for the nominal formula (Zn1-x-yAlxIny)O, with x=0.02, y=0.05. It has been studied that power factor is a function of c/a ratio which is further a function of dopant concentration. The resistivities of all the compositions have been tuned and the lowest resistivity of the order 1.997 mΩ.cm at 692.3°C has been observed for the nominal formula (Zn1-x-yAlxIny) with x=0.02, y=0.01. These tuned resistivities will be helpful for future thermoelectric devices.

Right Heterogeneous Microstructure for Achieving Excellent Thermoelectric Performance in Ca0.9R0.1MnO3−δ (R = Dy, Yb) Ceramics

Perovskite manganite Ca0.9R0.1MnO3-δ (R = Dy, Yb) ceramics have been synthesized by a traditional solid-state reaction with multicalcination processes. A heterogeneous microstructure including large and small micrometer-sized grains, coherent interfaces, and oxygen defects has been formed with optimized calcination time. The carrier concentration of the third-calcined samples is enhanced approximately 3 times compared with those synthesized through conventional methods. Thus, the electrical resistivity of the third-calcined Ca0.9R0.1MnO3-δ (R = Dy, Yb) ceramic samples obviously decreases, leading to a higher power factor. Additionally, the thermal conductivity is also reduced by multiscale scattering of the heterogeneous structure. The lowest lattice thermal conductivities of Dy- or Yb-doped samples are 1.24 and 1.22 W m-1 K-1, respectively. Thus, the high thermoelectric performance for Ca0.9R0.1MnO3-δ (R = Dy, Yb) has been achieved by the multicalcination process. The highest figure of merit is almost 30% higher than that of the first-calcined samples. Therefore, a heterogeneous microstructure formed by optimized multicalcination can effectively optimize the thermoelectric performance of oxides.