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The 0.97(Na0.5K0.5)(Nb1−xSbx)O3‐0.03CaZrO3 ceramic with x = 0.09 exhibits a high d33 of 518 pC/N and a strain of 0.13% at 4.0 kV/mm owing to its orthorhombic‐pseudocubic polymorphic phase boundary (PPB) structure. However, these values decreased considerably above 90°C owing to its low Curie temperature (TC), indicating that its thermal stability is not sufficient for practical applications. Li2O was added to the specimen with x = 0.11 to improve its thermal stability of the strain and d33 by increasing the TC without degrading the actual d33 and strain values. The 0.97(Li0.04Na0.46K0.5)(Nb0.89Sb0.11)O3‐0.03CaZrO3 ceramic, having an orthorhombic‐tetragonal PPB structure, exhibits a d33 of 502 pC/N and a strain of 0.16%. This large strain was maintained up to 150°C and the d33 slightly decreased to 475 pC/N at 130°C. Therefore, this lead‐free ceramic displays excellent piezoelectric characteristics with improved thermal stability, indicating that it can be applied to piezoelectric actuators. [ABSTRACT FROM AUTHOR]

Abstract: CuO‐added 0.96(Na0.5K0.5)(Nb1‐xSbx)O3‐0.04SrTiO3 ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤  x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤  x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb5+ ions. The specimens with 0.05 ≤  x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d33 values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d33 of 358 pC/N, kp of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm. [ABSTRACT FROM AUTHOR]

(Na1-xKx)NbO3 (NKN) platelets synthesized at 600°C for 12 h have an Amm2 orthorhombic structure. However, the structure of NKN platelets synthesized at 500°C is a mixture of R3m rhombohedral and Amm2 orthorhombic structures. The formation of a rhombohedral structure is attributed to the presence of OH- and H2O defects in the NKN platelets. The piezoelectric strain constant (d33) of NKN platelets synthesized at 600°C for 12 h is 100 pmV- 1, whereas that of NKN platelets synthesized at 500°C is lesser (50 pmV-1) due to the presence of these defects. Piezoelectric nanogenerators (PNGs) are fabricated using composites consisting of NKN platelets and polydimethylsiloxane. A large output voltage of 25 V and output current of 2.7 lA were obtained for the PNG with NKN platelets synthesized at 600°C for 6 h. This PNG shows a high output electrical energy of 3.0 lW at an external load of 5.1 MO. [ABSTRACT FROM AUTHOR]

A specimen having a stoichiometric composition of KSbO3·(KSb) calcined at 800°C has an R3 rhombohedral structure (RS), and changes to a Pn3 cubic structure (CS) when calcined at 1100°C. Finally, a <111>-oriented rhombohedral phase is formed in the specimen calcined at 1230°C. K/Sb ratio decreases from 1.0 in RS, 0.93 in CS, and finally to 0.85 in <111>-oriented rhombohedral phases. On the other hand, a specimen having a K-excess composition of K1.1SbO3 calcined at 800°C shows a RS that is maintained in the K-excess specimen calcined at 1230°C. The composition of these specimens is very close to KSb. Therefore, the RS with a space group of R3 is a stable form of KSbO3. The formation of Pn3 cubic and <111>-oriented R3 phases can be explained by the evaporation of K2O during the calcination process at temperatures above 1100°C. [ABSTRACT FROM AUTHOR]

Cordierite honeycomb ceramics are sintered under a range of sintering atmosphere and temperature conditions. The linear thermal expansion coefficient (CTE) is measured along the extrusion direction. The samples sintered in an enclosed crucible have a much lower CTE than those sintered in open air. The CTE decreases with increasing sintering temperature up to 1450 °C. The polymorphic phases, texture, amorphous phase, impurity crystals, and porosity are analyzed using scanning electron microscopy, HR‐TEM, porosimeter, and Rietveld refinement method. The sintered samples consist of two polymorphic phases: indialite (hexagonal symmetry) and cordierite (orthorhombic symmetry). Both the volume % of the cordierite phase and the crystal texture increase with increasing sintering temperature. The orthorhombic distortion of cordierite from the hexagonal lattice (indialite) increases with increasing sintering temperature. The characteristic six‐membered ring of the (Si,Al)‐O4 tetrahedra in the cordierite structure shows substantial changes in the bond length due to Al‐Si ordering. Amorphous phase and impurity crystal phases such as silimanite and spinel remain at temperatures as high as 1450 °C. The effect of the polymorphic phases, the degree of texture, amorphous phase, impurity crystal phases, and the orthorhombic distortion is discussed in relation to the CTE characteristics of honeycomb. The sintered honeycomb consists of two polymorphic phases, indialite (hexagonal symmetry) and cordierite (orthorhombic symmetry). The volume % of cordierite phase and the crystal texture increase with increasing sintering temperature. The thermal expansion coefficient (CTE) reduces with the sintering temperature. The orthorhombic distortion originates from Al‐Si ordering. Amorphous and silimanite phases are ascribed to higher CTEs of the samples sintered in open air. [ABSTRACT FROM AUTHOR]