Abstract: A piezoelectric ceramic comprising a perovskite composite oxide of an ABO3 composition containing Pb in the A-site and Zr and Ti in the B-site, wherein when the total amount of the element species constituting the B-site of the perovskite composite oxide in the ceramic is set to be one mol, an average valency of the element species constituting the B-site is in a range of from 4.002 to 4.009. The piezoelectric ceramic can be fired at a low temperature, has a high Curie temperature and a high piezoelectric distortion constant, as well as excellent durability and reliability against high temperatures.

Abstract: A laminated piezoelectric actuator comprising external electrodes formed on the side surfaces of an actuator body constituted by plural piezoelectric layers and plural internal electrode layers alternatingly laminated in the direction of height, external electrodes connecting the ends of said internal electrode layers, the internal electrode layers neighboring one another with the piezoelectric layers sandwiched among them of one side constituting first electrode layers and the internal electrode layers of the other side constituting second electrode layers, wherein the external electrodes include a first external electrode connecting the ends of the first electrode layers, and a second external electrode connecting the ends of the second electrode layers and is formed on a side surface of the actuator body different from the side surface on where the first external electrode is formed, insulating blocks are arranged between the first external electrode and the ends of the second electrode layers, and between

Abstract: A dielectric material having a low dielectric loss factor for high-frequency use, which comprises a sintered product of silicon nitride chiefly composed of silicon nitride and containing at least oxygen as an impurity component or oxygen as an impurity component and a compound of an element of the Group 3a of periodic table, wherein said sintered product contains aluminum in an amount which is not larger than 2% by weight reckoned as an oxide thereof having relative densities of not smaller than 97% and has a dielectric loss factor at 10 GHz ofnot larger than 5.times.10.sup.-4. The dielectric material has excellent mechanical properties such as large strength and excellent chemical stability, features small dielectric loss factor in high-frequency regions, and is suited for use as a material for high-frequency oscillators, antennas, filters and electronic circuit boards.

Abstract: A sintered product of silicon nitride containing not smaller than 70 mol % of a .beta.-silicon nitride as well as an element of the Group 3a at least including Lu of periodic table and impurity oxygen, wherein when the content of the element of the Group 3a of periodic table and the content of the impurity oxygen are, respectively, expressed being reckoned as the amount of an oxide of the element of the Group 3a of periodic table (RE.sub.2 O.sub.3) and as the amount of SiO.sub.2 of impurity oxygen, their total amount is from 2 to 30 mol %, the molar ratio (SiO.sub.2 /RE.sub.2 O.sub.3) of the amount of the element of the Group 3a of periodic table reckoned as the oxide (RE.sub.2 O.sub.3) thereof to the amount of impurity oxygen reckoned as SiO.sub.2 is from 1.6 to 10, and the intergranular phase of the sintered product chiefly comprises a crystal phase consisting of the element of the Group 3a of periodic table, silicon and oxygen and a process for producing the same.

Abstract: A silicon nitride-silicon carbide composite sintered material which comprises 100 parts by weight of a silicon nitride component containing 92 to 99.5 mol % of silicon nitride including excessive oxygen and 0.5 to 8 mol % of the elements of Group IIIa in the Periodic Table as corresponding oxides thereof and 1 to 100 parts by weight of a silicon carbide component in a dispersed state, wherein the silicon nitride component has an average particle size of 1 .mu.m or less and an average aspect ratio of 2 to 10, and the silicon carbide component has an average particle size of 1 .mu.m or less, moreover, the total amount of Al, Mg, Ca respectively contained in the sintered material as calculated as oxides thereof is 0.5% by weight or less, and a manufacturing method thereof.According to the above-mentioned composite sintered material, it becomes possible to suppress deterioration of strength at 1400.degree. C. and realize excellent creep properties.

Abstract: Disclosed is a silicon nitride sintered body comprising 70 to 99 mole % of silicon nitride, 0.1 to 5 moles % of a rare earth element oxide and up to 25 moles % of silicon oxide and having a silicon oxide-to-rare earth element oxide molar ratio of from 2 to 25, wherein silicon nitride crystal grains have a fine acicular structure having an average particle major axis of up to 7 .mu.m and an average aspect ratio of at least 3.