A method capable of obtaining pure single phase hexagonal diamond in an industrially usable size (bulk) is provided. Highly oriented and highly crystallized graphite having a mosaic spread of 5 or less is used as a starting material, and is subjected to a temperature ranging from 1000 to 1500 C. at a pressure ranging from 20 to 25 GPa. The size of the bulk sintered body of pure single-phase hexagonal diamond obtained by this method depends on the size of the starting graphite. However, as long as the pressure and temperature can be entirely provided (i.e., as long as the adequate high pressure and temperature are applied to the sample chamber of high pressure apparatus), any desired size can be obtained.

An alumina sintered body according to the present invention has a degree of c-plane orientation of 90% or more as determined by Lotgering's method from an X-ray diffraction profile obtained by irradiating a plate surface with X-rays in a range of 2=20 to 70. The alumina sintered body has no pores when a cross-sectional surface formed in a direction perpendicular to the plate surface is polished using an Ar.sup.+ ion beam and a mask and is examined under a scanning electron microscope at a magnification of 5,000 times. The alumina sintered body has a total mass fraction of impurity elements other than Mg and C of 100 ppm or less. This alumina sintered body has a high degree of orientation, high density, and high purity and thus has a higher optical translucency than those known in the art.

Provided are a method for producing a single crystal diamond capable of synthesizing a single crystal diamond having excellent durability at a low cost in a short time, and the single crystal diamond. The method for producing the single crystal diamond employs a high-temperature and high-pressure method, and the single crystal diamond is synthesized by exposing raw materials composed of amorphous carbon and a carbon compound to a pressure and a temperature in a thermodynamically stable region of the diamond in a carbon phase equilibrium diagram.

Provided are a method for producing a single crystal diamond capable of synthesizing a single crystal diamond having excellent durability at a low cost in a short time, and the single crystal diamond. The method for producing the single crystal diamond employs a high-temperature and high-pressure method, and the single crystal diamond is synthesized by exposing raw materials composed of amorphous carbon and a carbon compound to a pressure and a temperature in a thermodynamically stable region of the diamond in a carbon phase equilibrium diagram.

A method for producing an oriented sintered body according to the present invention includes the steps of: (a) preparing a multilayer body, the multilayer body including a layer including a fine raw-material powder and a layer including a plate-like raw-material powder which are alternately stacked each other, particles of the plate-like raw-material powder being arranged such that surfaces of the particles of the plate-like raw-material powder extend along a surface of the layer including a fine raw-material powder; and (b) sintering the multilayer body.

A method for producing an oriented sintered body according to the present invention includes the steps of: (a) preparing a multilayer body, the multilayer body including a layer including a fine raw-material powder and a layer including a plate-like raw-material powder which are alternately stacked each other, particles of the plate-like raw-material powder being arranged such that surfaces of the particles of the plate-like raw-material powder extend along a surface of the layer including a fine raw-material powder; and (b) sintering the multilayer body.

An oriented alumina substrate for epitaxial growth according to an embodiment of the present invention includes crystalline grains constituting a surface thereof, the crystalline grains having a tilt angle of 1 or more and 3 or less and an average sintered grain size of 20 m or more.

An oriented alumina substrate for epitaxial growth according to an embodiment of the present invention includes crystalline grains constituting a surface thereof, the crystalline grains having a tilt angle of 0.1 or more and less than 1.0 and an average sintered grain size of 10 m or more.

The present invention provides: an electrophotographic photosensitive member which reduces image defects due to ghosting not only under a normal temperature and normal humidity environment but also even under a low temperature and low humidity environment; and a novel phthalocyanine crystal. The electrophotographic photosensitive member of the present invention comprises a photosensitive layer which comprises a phthalocyanine crystal in which a N,N-dimethylformamide is contained. The content of the N,N-dimethylformamide is 0.1% by mass or more and 1.5% by mass or less based on the phthalocyanine crystal.

The present invention provides: an electrophotographic photosensitive member which reduces image defects due to ghosting not only under a normal temperature and normal humidity environment but also even under a low temperature and low humidity environment; and a novel phthalocyanine crystal. The electrophotographic photosensitive member of the present invention comprises a photosensitive layer which comprises a phthalocyanine crystal in which a N,N-dimethylformamide is contained. The content of the N,N-dimethylformamide is 0.1% by mass or more and 1.5% by mass or less based on the phthalocyanine crystal.