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InGaO3(ZnO)m (m = 1, 2, 3, 4, and 5) ceramics are a series of n-type oxide thermoelectric materials with layered structures and low thermal conductivities. Herein, InGaO3(ZnO)m (m = 1, 2, 3, 4, and 5) ceramics were fabricated by spark plasma sintering (SPS). Two different trends in the thermoelectric properties of the InGaO3(ZnO)m (m = 1, 2, 3, 4, and 5) ceramics were observed depending on the odevity of the m value. The InGaO3(ZnO) sample exhibited a relatively high electrical conductivity and was therefore selected for vacuum annealing to further improve the electrical transport performance. Oxygen vacancy defects were introduced to the matrix during the annealing procedure, which improved the thermoelectric performance. A maximum ZT of 0.45 was obtained at 973 K for the InGaO3(ZnO) sample with a 96 h vacuum annealing treatment, which is 30 times higher than that of the pristine sample.

As a novel candidate of thermal barrier coatings materials proposed recently, rare earth tantalates (RETaO4) are attractive series because of its excellent attributes. With respect to RETaO4 compound, it exists at least three types of polymorphs and two phase-transformation mechanisms. In this paper, the monoclinic (Y1-xYbx)TaO4 compounds with diverse space groups are investigated systematically, and contents involve phase, microstructural and thermophysical properties’ evolution with the changes of composition and structure. The primary purpose of this paper is to optimize the thermophysical properties of (Y1-xYbx)TaO4 ceramics by adjusting the Y/Yb ratio, and further physical mechanisms of its heat transfer are also revealed.

In this paper, a series of solid solutions ceramics of (AlxGd1-x)3TaO7 (x = 0, 0.01, 0.03, 0.05) were synthesized via solid-state reaction. X-ray diffraction (XRD) and Raman spectroscopy analysis indicated that the crystal structure of (AlxGd1-x)3TaO7 ceramics is weberite in spite of the content of Al3+ is up to 5 mol.%. The thermal conductivities of (AlxGd1-x)3TaO7 ceramics range from 1.37 W∙m−1 K−1 to 1.47 W∙m−1 K−1 at 900 ℃, which is much lower than that of 7–8 YSZ (about 2.5 W∙m−1 K−1). The thermal expansion coefficients (TECs) of (AlxGd1-x)3TaO7 ceramics vary in the range of 6–10 × 10-6 K-1 within the temperature range 100–1200 ℃, and the values are close to the TECs of 7–8 YSZ. Given the low thermal conductivity and high thermal expansion coefficients of (AlxGd1-x)3TaO7 ceramics, they have the potential to be the next generational thermal barrier coating materials.

A morphotropic phase boundary (MPB) between rhombohedral (R) and tetragonal (T) phases was identified in a few (0.9-x)NaNbO3-0.1BaTiO3-xABO3 (x = 0–0.05) lead-free systems. Critical roles of R-phase inducers were specially evaluated in terms of phase boundary position, microstructure and piezoelectric responses. The results indicate not only the tolerance factor of the ABO3 additive but also its ferroelectricity and corresponding volume change would influence the formation of phase boundary and further determine dielectric and ferroelectric responses. The piezoelectric coefficient d33 of MPB compositions was compared with theoretically-calculated d33-cal according to d33 = 2Pr·e33·Q33, demonstrating that the piezoelectric response of these systems should be determined by combined effects of the phase coexistence, nano-scale domains and particularly enhanced dielectric responses. The largest d33 ∼305 pC/N, the highest e33T/eo ∼2815 and the lowest Pr ∼14.7 μC/cm2 were achieved in the MPB composition with 3.75% SrZrO3. These experimental results provide a valuable reference for designing new NaNbO3-based lead-free piezoelectric materials.

Modification process has been conducted on commercial nuclear graphite IG-110 (Toyo Tanso Co., Ltd., Japan) by impregnation and pyrolysis of polycarbosilane (PCS) solution for getting the modified IG-110 (M-IG-110) coated by dense SiC coating for molten salt reactor. The microstructure and properties of graphite were systematically investigated and compared before and after the modification process. Results indicated that the M-IG-110 possessed of more excellent integrated properties including molten salt barrier property and oxidation resistance than bare IG-110 due to the filling effect of SiC particles in the pores of M-IG-110 and dense SiC coating adhering to the surface of M-IG-110. The fluoride salt infiltration amount of M-IG-110 under 5 atm was only 1.1 wt%, which was much less than 14.9 wt% for bare IG-110. The SiC coating derived from PCS exhibited remarkable compatibility with graphite substrate under high temperature and gave rise to excellent oxidation resistance of M-IG-110.

Cu-Se compounds have attracted more attentions as a low-cost, low toxicity thermoelectric materials. In this work, p-type Cu 2 Se x compound powders were prepared by solution syntheses, including the wet chemistry method and hydrothermal synthesis method. The reaction mechanisms were investigated, showing that the NaOH contents affected the phase structure of the final product. Polycrystalline Cu 2 Se x bulk materials were obtained by densifying the powders using spark plasma sintering (SPS) and obtained the maximum ZT value of 0.75 at 623 K, which is currently the highest reported value for the Cu-Se system at this temperature. We also found that the introduced oxides could suppress the long-range migration of Cu ions in Cu-Se system to avoid the decomposition of the materials.

Various strain contributions of (Na 0.52 K 0.48 − x )(Nb 0.92 − x Sb 0.08 )O 3 − xLiTaO 3 ceramics in the proximity of orthorhombic (O) and tetragonal (T) polymorphic phase boundary (PPB) were quantitatively resolved by means of synchrotron x-ray diffraction together with macroscopic strain measurements. Compared with O-rich compositions with a governing mechanism of intrinsic lattice strains, T-rich compositions exhibited a dominant strain mechanism from reversible domain switching. Quantitative analysis of diffraction data suggested that extrinsic strain contributions should depend on not only the lattice distortion δ, but also the poling texture Δf, phase content (for PPB compositions) and domain types. Smaller lattice distortion and higher poling texture tended to enhance the number of irreversible domain switching in O-rich compositions, thus leading to larger fraction of intrinsic lattice strain contribution. The calculated results demonstrated that the product of two parameters Δf and δ would give a reliable estimation of domain-switching strains for T-phase compositions but an overestimation for O-phase compositions.

The electrical properties and microstructures of (1 − x ) Bi 1/2 Na 1/2 TiO 3 – x SrTiO 3 (BNT-ST100 x , 0.20 ≤ x ≤ 0.30) piezoceramics with different grain size distributions were investigated. The critical region separating the ferroelectric from ergodic relaxor is located around x = 0.26. Strains up to 0.2% could be achieved under a low driving fields ( E S max /E max >1000 pm/V. The electrostrain was largely depended on the grain size and an increment of strain up to ∼38% can be realized by increasing the grain size from 5 μm to 13 μm in the BNT-ST26 samples. The results indicate that the field-induced strain performance of BNT-based incipient piezoelectric ceramics can be tailored via microstructure modifications, an alternative strategy to enhance the electromechanical properties.

High transparency ytterbium doping yttria (Yb:Y2O3) ceramics were fabricated by vacuum sintering. The influence of temperature and doping concentration on optical and thermal properties of Yb:Y2O3 ceramics were evaluated. The increased Yb doping concentration causes the red-shift of absorption edge. The intensities of absorption peaks increase linearly with Yb3+ ion concentration, and the absorption cross-section at ∼978 nm is calculated to be 1.15 × 10−20 cm2. When Yb3+ doping content is 5.0 at.%, the strongest peak centers at the wavelength of 1030 nm with the full width at half maximum (FWHM) of 17 nm, and stimulated emission cross-section is measured to be 1.58 × 10−20 cm2. Both absorption coefficient and fluorescence lifetime increase with increasing Yb3+ concentration. The optimum doping concentration of Yb3+ ion in Y2O3 transparent ceramic is in the range of 5.0–7.0 at.%. For 5.0 at.% Yb:Y2O3 transparent ceramic, as temperature increases from 10 K to room temperature (RT), the fluorescence intensity decreases and the peaks are broaden.

This work investigated the enhanced sintering and electrical properties of (Ba 0.95 Ca 0.05 )(Ti 0.90 Sn 0.10 )O 3 - x Li 2 O (BCTSLi x , x = 0, 1, 2, 3, 4, 5 and 6 mol%) lead-free piezoelectric ceramics benefiting from the Li 2 O addition. Highly dense BCTS ceramics with good piezoelectric properties were fabricated at reduced sintering temperatures by adding a small amount of Li 2 O. It was found that the sintering densification is promoted mainly by reaction liquid phase at the early sintering stage and the formation of oxygen vacancies should be considered as an additional factor. The coexistence of R and T phases was confirmed by the Raman spectrum at a temperature range from−50 °C to 40 °C as x = 2 and at room temperature for all other Li 2 O added samples, while their specific ratio of R to T phase decreases with increasing Li 2 O addition. Better properties with d 33 = 457 pC/N, k p = 25.18% and Q m = 491 were obtained when adding 4 mol% Li 2 O, which are attributed dominantly to the appropriate specific ratio of R to T phase because of the similar grain size and density for samples at 3 ≤ x ≤ 6.

Dense Li/Ta-codoped KNN-based piezoceramics with d(33)* up to 375 pm/V were successfully fabricated by conventional sintering at a temperature as low as 900 degrees C by using LiF as a sintering additive. The reduction of densification temperature up to 200 degrees C was realized by a transient liquid phase sintering mechanism, consequently no grain boundary phase was observed in the sintered samples. It was found that the addition of LiF could further shift down the tetragonal orthorhombic transition point (TT-O), indicating that a small amount of Li+ could diffuse into the A-site of KNN matrix. The introduction of LiF enhanced the linearity of strain curves of the ceramics, which is unambiguously in favor for the actuator application. The present work reveals that low-temperature sintered LiF-doped KNN-based piezoceramics demonstrates promising potential in multilayer-structured actuator applications. (C) 2013 Elsevier Ltd. All rights reserved.

A small amount of BiFeO3 (BF) was incorporated into lead-free Li0.03(Na0.53K0.48)0.97Nb0.8Ta0.2O3 (LKNNT) piezoceramics for the purpose of property improvement via phase structure control. It was found that the addition of BF not only induced a series of phase transformations from orthorhombic to tetragonal and further to pseudocubic in LKNNT ceramics, but also enhanced its sintering densification behavior. Even tiny amount of BF addition down to 0.5 mol% could change the room-temperature phase structure from a dominant orthorhombic state to the coexistence of orthorhombic and tetragonal phases, resulting in peak piezoelectric properties of d 33 * ∼ 340 pm/V , kp ∼ 47.0%. When the amount of BF was increased to 0.75 mol%, the tetragonal phase became dominant in the modified LKNNT ceramics, which exhibited excellent temperature stability, despite its slightly lowered piezoelectric coefficients.

XRD and Raman scattering experiments revealed an interesting finding that phase structure changed from orthorhombic to tetragonal symmetry when pulverizing (Li,Ta)-doped (K,Na)NbO3 lead-free piezoelectric ceramics (sintered body) to powder. Both orthorhombic and tetragonal phases coexist in the Li0.05(Na0.51K0.49)0.95Nb0.80Ta0.20O3.00 (LKNNT) sintered bulk sample at room temperature, but almost only the tetragonal phase is observed in the ground powder. In addition, annealing experiment enhanced the formation of tetragonal phase and improved the temperature stability of piezoelectricity. It is revealed that the internal stress existing in the LKNNT ceramics favors the formation of orthorhombic phase, which transfers to tetragonal phase when the stress was released.

Lead zirconate titanate (PZT) films with composition near the morphotropic phase boundary were fabricated on Pt(111)/Ti/SiO 2 /Si(100) using sol-gel method, and the pyrolysis temperature effects on the preferential orientation and ferroelectric properties of PZT films were investigated. It has been found that the PZT films pyrolyzed at 450 °C and then annealed at 650 °C shown a dominated (100) orientation, whereas the pyrolysis treatment at lower or higher temperatures favored the (111) orientation. Different pyrolysis temperatures also lead to differences in electrical properties, including dielectric constant, polarization values, leakage current and fatigue behavior.

The PZT/Pt composites with various compositions were fabricated by using powder processing, and their mechanical, dielectric, piezoelectric and elastic properties were evaluated with the purpose to develop piezoelectric actuators with functionally graded microstructure (FGM). The piezoelectric and dielectric constants of the PZT/Pt composites decreased monotonously with increasing Pt content, whereas the addition of the Pt particles greatly improved the mechanical properties, particularly the fracture toughness in the composites. Miniature bimorph-type FGM actuators that consist of a composite internal-electrode (70 vol.%PZT/30 vol.%Pt) and three piezoelectric layers (100 vol.%PZT to 80 vol.%PZT/20 vol.%Pt) were fabricated by powder stacking and normal sintering techniques. The electrically-induced deflection characteristics of such an FGM actuator were measured with electric strain gages mounted on the top and bottom surfaces of the actuators, and the measured data were consistent with the analytical results given by the modified classical lamination theory model (CLT).

Reaction-bonded Si 3 N 4 composites reinforced by whisker-like SiC rod particulates have been fabricated by nitriding SiC rod -containing Si powder compacts, which were presintered to a controlled density by spark plasma sintering (SPS). The effects of processing parameters, including presintered density, SiC rod content, nitriding temperature, atmosphere pressure and heating rate on the nitridation reaction were investigated. It was found that the addition of SiC rod to Si powders led to easier control of complete nitridation compared to the case of pure Si powder compacts, probably because the SiC rod not only acted as diluting filler to suppress the rapid rise in temperature resulting from an SHS-like reaction between Si and N 2 , but also provided paths for diffusion of reactant gases. The density of the reaction-bonded Si 3 N 4 –50 vol% SiC rod composites was increased up to near 90% which is quite a lot higher than that of conventional reaction-bonded Si 3 N 4 ceramics, by using SPS to improve the density prior to nitridation. The relative density increased from ∼70 to 90% after the nitridation without appreciable dimensional change, being characteristic of reaction-sintering. As the reinforcement in the reaction products, the SiC rod improved Young's modulus and bending strength both at ambient and elevated temperatures, as well as thermal and electric conductivity.