A sintered body of the present invention contains yttrium oxyfluoride. The yttrium oxyfluoride is preferably YOF and/or Y.sub.5O.sub.4F.sub.7. The sintered body of the present invention preferably contains 50% by mass or more of yttrium oxyfluoride. The sintered body of the present invention has a relative density of preferably 70% or more and an open porosity of preferably 10% or less. Furthermore, the sintered body of the present invention has a three-point bending strength of preferably 10 MPa or more and 300 MPa or less.

Bulk iron nitride can be synthesized from iron nitride powder by spark plasma sintering. The iron nitride can be spark plasma sintered at a temperature of less than 600 C. and a pressure of less than 600 MPa, with 400 MPa or less most often being sufficient. High pressure SPS can consolidate dense iron nitrides at a lower temperature to avoid decomposition. The higher pressure and lower temperature of spark discharge sintering avoids decomposition and limits grain growth, enabling enhanced magnetic properties. The method can further comprise synthesis of nanocrystalline iron nitride powders using two-step reactive milling prior to high-pressure spark discharge sintering.

A method to produce high density, uniform lithium lanthanum tantalate lithium-ion conducting ceramics uses small particles that are sintered in a pressureless crucible that limits loss of Li.sub.2O.

The piezoelectric material of the present invention includes a main component composed of a perovskite-type metal oxide represented by Formula (1), at least one of Mn and Ni, and Mg. The content of Ni is 0 mol or more and 0.05 mol or less based on 1 mol of the perovskite-type metal oxide, and the content of Mn is 0 mol or more and 0.005 mol or less based on 1 mol of the perovskite-type metal oxide, provided that the content of Mn and the content of Ni are not simultaneously 0 mol. The content of Mg is 0.001 mol or more and 0.020 mol or less based on 1 mol of the perovskite-type metal oxide.

Formula (1): (Na.sub.xBa.sub.1-y)(Nb.sub.yTi.sub.1-y)O.sub.3 (where x is 0.83 or more and 0.95 or less, y is 0.85 or more and 0.95 or less, and x/y is 0.95 or more and 1.05 or less).

The present invention provides a piezoelectric material not containing lead and potassium, showing satisfactory insulation and piezoelectricity, and having a high Curie temperature. The invention relates to a piezoelectric material includes a main component containing a perovskite-type metal oxide represented by Formula (1): (Na.sub.xBa.sub.1-y)(Nb.sub.yTi.sub.1-y)O.sub.3 (wherein, 0.80?x?0.94 and 0.83?y?0.94), and an additive component containing at least one element selected from Mn and Ni, wherein the content of the Ni is 0 mol or more and 0.05 mol or less based on 1 mol of the perovskite-type metal oxide, and the content of the Mn is 0 mol or more and 0.005 mol or less based on 1 mol of the perovskite-type metal oxide.

A method of inhibiting an irregular aggregation of a nanosized powder includes (A) providing a nanosized ceramic powder to perform thereon a thermal analysis and thereby attain an endothermic peak temperature; (B) performing an impurity-removal heat treatment on the nanosized ceramic powder at a temperature higher than the endothermic peak temperature; (C) switching the nanosized ceramic powder from a temperature environment of the impurity-removal heat treatment to an environment of a temperature higher than a phase change temperature of the nanosized ceramic powder, followed by performing a calcination heat treatment on the nanosized ceramic powder in the environment of the temperature higher than the phase change temperature of the nanosized ceramic powder, wherein the nanosized ceramic powder skips the temperature environment between impurity-removal heat treatment and calcination heat treatment to shun generating a vermicular structure, avoid crystalline irregularity and abnormal growth, reduce particle aggregation, and achieve satisfactory distribution.

A zirconia sintered body is provided in which the strength between layers of powders is improved. A flexural strength of a test sample of the zirconia sintered body, measured pursuant to JISR1601, is not less than 1000 MPa. The test sample is formed by preparing a plurality of zirconia powders, each containing zirconia and preferably yttria as a stabilizer that suppresses phase transition of zirconia, the zirconia powders differing in a composition, layering the zirconia powders to form a zirconia composition, and sintering the zirconia composition to form a zirconia sintered body. The flexural strength is measured such that a load point is positioned at a boundary of the zirconia powders, the boundary traversing the test sample of the sintered body along a direction of load application.

A zirconia pre-sintered body suitable for dental milling, grinding and/or cutting can provide a sintered body in which the strength between layers of powders is improved. A flexural strength of a test sample of the zirconia sintered body, measured pursuant to JISR1601, is preferably not less than 1000 or 1100 MPa.

A SiAlON sintered body according to the present invention is represented by Si.sub.6-zAl.sub.zO.sub.zN.sub.8-z (0<z4.2) and has an open porosity of 0.1% or less and a relative density of 99.9% or more. A ratio of a total of intensities of maximum peaks of components other than SiAlON to an intensity of a maximum peak of the SiAlON in an X-ray diffraction diagram is 0.005 or less.

A lead-free lithium doped potassium sodium niobate piezoelectric ceramic material powdered form and having a single crystalline phase and uses thereof are described. Methods of making the said piezoelectric ceramic material are also described.