Provided is a self-supporting polycrystalline GaN substrate composed of GaN-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate. The crystal orientations of individual GaN-based single crystal grains as determined from inverse pole figure mapping by EBSD analysis on the substrate surface are distributed with tilt angles from the specific crystal orientation, the average tilt angle being 1 to 10. There is also provided a light emitting device including the self-supporting substrate and a light emitting functional layer, which has at least one layer composed of semiconductor single crystal grains, the at least one layer having a single crystal structure in the direction approximately normal to the substrate. The present invention makes it possible to provide a self-supporting polycrystalline GaN substrate having a reduced defect density at the substrate surface, and to provide a light emitting device having a high luminous efficiency.

Provided is a self-supporting polycrystalline GaN substrate composed of GaN-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate. The crystal orientations of individual GaN-based single crystal grains as determined from inverse pole figure mapping by EBSD analysis on the substrate surface are distributed with tilt angles from the specific crystal orientation, the average tilt angle being 1 to 10. There is also provided a light emitting device including the self-supporting substrate and a light emitting functional layer, which has at least one layer composed of semiconductor single crystal grains, the at least one layer having a single crystal structure in the direction approximately normal to the substrate. The present invention makes it possible to provide a self-supporting polycrystalline GaN substrate having a reduced defect density at the substrate surface, and to provide a light emitting device having a high luminous efficiency.

The invention is a process for producing crystals (polycrystals) that comprises steps of: evacuating, melting a raw material in a container by means of a resistance heater to form a skull layer of 5-10 mm, crystallizing a melt of the raw material, annealing and cooling the crystal, separating the skull layer. The container is coated inside with a metal foil having a thickness of 0.04-0.15 mm; the steps of melting the raw material, crystallizing, annealing and cooling the crystal are performed in a double-layered shell composed of the metal foil and the skull layer; after the crystallization step, the crystal is annealed in a separate annealing furnace. The invention allows to: prevent crystal cracking, produce the crystal without any internal stresses; reduce the raw material mass consumed to form the skull layer; increase the size and the weight of the produced crystal; reduce energy consumption.

The invention is a process for producing crystals (polycrystals) that comprises steps of: evacuating, melting a raw material in a container by means of a resistance heater to form a skull layer of 5-10 mm, crystallizing a melt of the raw material, annealing and cooling the crystal, separating the skull layer. The container is coated inside with a metal foil having a thickness of 0.04-0.15 mm; the steps of melting the raw material, crystallizing, annealing and cooling the crystal are performed in a double-layered shell composed of the metal foil and the skull layer; after the crystallization step, the crystal is annealed in a separate annealing furnace. The invention allows to: prevent crystal cracking, produce the crystal without any internal stresses; reduce the raw material mass consumed to form the skull layer; increase the size and the weight of the produced crystal; reduce energy consumption.

The present invention reports the general one-pot synthesis of IrNi-based nanostructures with unconventional hexagonal close-packed (hcp) phase. Notably, the as-synthesized hcp IrNi nanostructures demonstrate excellent catalytic performance towards electrochemical nitrite reduction for ammonia synthesis. Ex/in-situ characterizations and theoretical calculations reveal that the IrNi interactions within hcp IrNi-based nanostructures improve electron transfer to benefit both nitrite activation and active hydrogen generation, leading to a stronger reaction trend of NO.sub.2RR by greatly reducing energy barriers of rate-determining step.