Takeshi Mitsuoka

Processing of Piezoelectric (Li,Na,K)NbO3 Porous Ceramics and (Li,Na,K)NbO3/KNbO3 Composites

Porous Li0.06(Na0.5K0.5)0.94NbO3 (LNKN-6) ceramics with different pore volumes have been prepared using preceramic powder and phenol resin fiber (KynolTM) as a pore former. It was confirmed that the porous ceramics synthesized by the “two-stage firing method” suppressed the loss of alkali elements from the porous body during heat treatment. The porous LNKN-6 ceramics were then converted to LNKN-6/KNbO3 composites through soaking and heat treatment using a sol–gel precursor source composed of KNbO3 to form 3–3-type composites. The microstructure, dielectric, and piezoelectric properties of the porous LNKN-6 ceramics and LNKN-6/KNbO3 composites were characterized and compared. The LNKN-6/KNbO3 composites had a hollow structure whose pores in the region near the surface were filled and coated with KNbO3 precipitates; however, a large amount of residual air was trapped in the pores inside the composites. As a result, the LNKN-6/KNbO3 composites fabricated using 30 vol % KynolTM showed an enhanced piezoelectric voltage output coefficient (g33) of 63.0×10-3 V·m/N, compared with monolithic LNKN-6 ceramics having a g33 of 30.2×10-3 V·m/N.

Effect of Pore Shape on the Electrical Property of Porous LNKN Piezoceramics

Porous Li 0.06 (Na 0.5 K 0.5 ) 0.94 NbO 3 (LNKN-6) piezoceramics with different pore shapes and volumes have been fabricated by sintering a mixture of calcinated LNKN-6 powder and volatilizable pore formers of phenol resin fibers (Kynol™) or plastic spheres [poly(methyl methacrylate)] (PMMA). Kynol™ fiber was shown to more effective for inducing open-pore formation in the ceramics than PMMA sphere. The porous LNKN-6 ceramics prepared using Kynol™ fiber demonstrated lower dielectric loss, higher piezoelectric constant (d 33 ), and higher piezoelectric voltage coefficient (g 33 ) than those prepared using PMMA sphere. The effect of pore shape on the electrical property was investigated.

Characteristic Design of Microwave Dielectric Materials by Using Self-Flux Compositions

In order to improve the sinterability and controllability of dielectric properties, we focused on self-flux composition. In the case of Ba(Mg1/3Nb2/3)O3, we selected Ba(1-b)NbbOd as self-flux system and investigated correlations between Q-factor and the b value. Interestingly, high Q-value was obtained only at the b=0.45. Moreover, the dielectric constant and tf change linearly by the quantity of Ba0.55Nb0.45Od under keeping up high-Q value. As a result, it was indicated that the dielectric properties could be controlled by the assumption of stoichiometric composition and liquid phase consisted by self-flux.

Fracture response of structural ceramics combined with electrical functions

Fiber reinforced Si3N4 matrix ceramics combined with electrical conductive phases of carbon fiber (Cf) and WC were fabricated by hot pressing. The function of fracture response of the materials was evaluated by measuring simultaneously load-deflection and electrical resistance – deflection curves in four points bending tests. The electrical resistance change closely corresponded to the fracture behavior of the materials. The variation in electrical conductive phases facilitates the detection of different stages of fracture in fiber reinforced ceramic materials.