Provided are a piezoelectric material, a piezoelectric member, a piezoelectric element and a pressure sensor that can be used in high-temperature environments. The piezoelectric material is composed of Sr-substituted akermanite represented by Ca.sub.(2-x)Sr.sub.xMgSi.sub.2O.sub.7 (0.1≤x≤0.6).

A method for preparing a large-size two-dimensional layered metal thiophosphate crystal includes the following steps: 1) weighing raw materials of indium spheres, phosphorous lumps and sulfur granules according to a predetermined amount and proportion, mixing them, and using iodine as a transport agent and potassium iodide as a molten salt; 2) adding the raw materials, the iodine and the potassium iodide to a reaction vessel together, and vacuum sealing it under a certain pressure, and then subjecting it to a high-temperature reaction; 3) taking out the products after the reaction, and washing the products to remove the residual iodine and potassium iodide and obtain large-size two-dimensional layered metal thiophosphate crystals. This method is simple and highly efficient.

A method for preparing a large-size two-dimensional layered metal thiophosphate crystal includes the following steps: 1) weighing raw materials of indium spheres, phosphorous lumps and sulfur granules according to a predetermined amount and proportion, mixing them, and using iodine as a transport agent and potassium iodide as a molten salt; 2) adding the raw materials, the iodine and the potassium iodide to a reaction vessel together, and vacuum sealing it under a certain pressure, and then subjecting it to a high-temperature reaction; 3) taking out the products after the reaction, and washing the products to remove the residual iodine and potassium iodide and obtain large-size two-dimensional layered metal thiophosphate crystals. This method is simple and highly efficient.

The purpose of diffusion assisted crystal hydrothermal growth is to facilitate a greatly increased crystal growth rate that would save time that is precious in such a material and manpower costly process. The assisted crystal growth itself requires the utilization of a piezoelectric shaker connected to the autoclave in which most industrial hydrothermal crystals are grown. The waveform can be modulated to induce transport of nutrient in a singular direction, customized to the topology of the apparatus. As it stands currently, the growth of most crystals that require autoclaves for their production can take anywhere from 3 months to up to 2 years, and accordingly carries many costs, particularly electricity and supervision of the autoclave(s), and other issues that may arise during the growth. While the product of this labor results in high-quality crystals, in reality, these are not at all what is needed outside of the laboratory environment. Using the assisted crystal hydrothermal growth process, average crystal growth can be cut in half, with the resulting crystals consequently being of a slightly lower quality, though still sufficient for most engineering purposes. Another advantage of using a piezoelectric shaker is that an additional sensor can be added to the autoclave to monitor the health of the autoclave using trending data obtained during the growth.

The purpose of diffusion assisted crystal hydrothermal growth is to facilitate a greatly increased crystal growth rate that would save time that is precious in such a material and manpower costly process. The assisted crystal growth itself requires the utilization of a piezoelectric shaker connected to the autoclave in which most industrial hydrothermal crystals are grown. The waveform can be modulated to induce transport of nutrient in a singular direction, customized to the topology of the apparatus. As it stands currently, the growth of most crystals that require autoclaves for their production can take anywhere from 3 months to up to 2 years, and accordingly carries many costs, particularly electricity and supervision of the autoclave(s), and other issues that may arise during the growth. While the product of this labor results in high-quality crystals, in reality, these are not at all what is needed outside of the laboratory environment. Using the assisted crystal hydrothermal growth process, average crystal growth can be cut in half, with the resulting crystals consequently being of a slightly lower quality, though still sufficient for most engineering purposes. Another advantage of using a piezoelectric shaker is that an additional sensor can be added to the autoclave to monitor the health of the autoclave using trending data obtained during the growth.

In a single-crystal diamond material, a concentration of non-substitutional nitrogen atoms is not more than 200 ppm, a concentration of substitutional nitrogen atoms is lower than the concentration of the non-substitutional nitrogen atoms, and the single-crystal diamond material has a crystal growth main surface having an off angle of not more than 20°. A perforated tool includes a single-crystal diamond die, wherein in the single-crystal diamond die, a concentration of non-substitutional nitrogen atoms is not more than 200 ppm, a concentration of substitutional nitrogen atoms is lower than the concentration of the non-substitutional nitrogen atoms, and the single-crystal diamond die has a low-index plane represented by a Miller index of not less than −5 and not more than 5 in an integer, a perpendicular line of the low-index plane having an off angle of not more than 20° relative to an orientation of a hole for wire drawing.

In a single-crystal diamond material, a concentration of non-substitutional nitrogen atoms is not more than 200 ppm, a concentration of substitutional nitrogen atoms is lower than the concentration of the non-substitutional nitrogen atoms, and the single-crystal diamond material has a crystal growth main surface having an off angle of not more than 20°. A perforated tool includes a single-crystal diamond die, wherein in the single-crystal diamond die, a concentration of non-substitutional nitrogen atoms is not more than 200 ppm, a concentration of substitutional nitrogen atoms is lower than the concentration of the non-substitutional nitrogen atoms, and the single-crystal diamond die has a low-index plane represented by a Miller index of not less than −5 and not more than 5 in an integer, a perpendicular line of the low-index plane having an off angle of not more than 20° relative to an orientation of a hole for wire drawing.

An apparatus for producing an SiC single crystal includes a crucible for accommodating an Si—C solution and a seed shaft having a lower end surface where an SiC seed crystal (36) would be attached. The seed shaft includes an inner pipe that extends in a height direction of the crucible and has a first passage. An outer pipe accommodates the inner pipe and constitutes a second passage between itself and the inner pipe and has a bottom portion whose lower end surface covers a lower end opening of the outer pipe. One passage of the first and second passages serves as an introduction passage where coolant gas flows downward, and the other passage serves as a discharge passage where coolant gas flows upward. A region inside the pipe that constitutes the introduction passage is to be overlapped by a region of not less than 60% of the SiC seed crystal.

A group 13 nitride crystal having a hexagonal crystal structure and containing at least a nitrogen atom and at least a metal atom selected from a group consisting of B, Al, Ga, In, and Tl. The group 13 nitride crystal includes a first region disposed on an inner side in a cross section intersecting c-axis, a third region disposed on an outermost side in the cross section and having a crystal property different from that of the first region, and a second region disposed at least partially between the first region and the third region in the cross section, the second region being a transition region of a crystal growth and having a crystal property different from that of the first region and that of the third region.

A group 13 nitride crystal having a hexagonal crystal structure and containing at least a nitrogen atom and at least a metal atom selected from a group consisting of B, Al, Ga, In, and Tl. The group 13 nitride crystal includes a first region disposed on an inner side in a cross section intersecting c-axis, a third region disposed on an outermost side in the cross section and having a crystal property different from that of the first region, and a second region disposed at least partially between the first region and the third region in the cross section, the second region being a transition region of a crystal growth and having a crystal property different from that of the first region and that of the third region.