A composite crucible for growing single crystals comprises an outer crucible of a first material, and an inner liner of a second material having a coefficient of thermal expansion differing from the first material. The outer crucible comprises an inside bore. The inner liner is disposed in the inside bore without diffusion bonding or chemical bonding between the outer crucible and the inner liner. In certain non-limiting embodiments, the first material is one of molybdenum and a molybdenum alloy, and the second material is one of tantalum, niobium, a tantalum alloy, and a niobium alloy.

To provide a method for producing a Group III element nitride crystal by growing it on a plane on the −c-plane side as a crystal growth plane. The present invention is a method for producing a Group III element nitride crystal, including a vapor phase growth step of growing a Group III element nitride crystal 12 on a crystal growth plane of a Group III element nitride seed crystal 11 by vapor deposition. The vapor phase growth step is a step of causing a Group III metal, an oxidant, and a nitrogen-containing gas to react with one another to grow the Group III element nitride crystal 12 or includes: a reduced product gas generation step of causing a Group III element oxide and a reducing gas to react with each other to generate a gas of a reduced product of the Group III element oxide; and a crystal generation step of causing the gas of the reduced product and a nitrogen-containing gas to react with each other to generate the Group III element nitride crystal 12. The crystal growth plane is a plane on the −c-plane side. A crystal growth temperature is 1200° C. or more. In the vapor phase growth step, the Group III element nitride crystal is grown in an approximately −c direction.

To provide a method for producing a Group III element nitride crystal by growing it on a plane on the −c-plane side as a crystal growth plane. The present invention is a method for producing a Group III element nitride crystal, including a vapor phase growth step of growing a Group III element nitride crystal 12 on a crystal growth plane of a Group III element nitride seed crystal 11 by vapor deposition. The vapor phase growth step is a step of causing a Group III metal, an oxidant, and a nitrogen-containing gas to react with one another to grow the Group III element nitride crystal 12 or includes: a reduced product gas generation step of causing a Group III element oxide and a reducing gas to react with each other to generate a gas of a reduced product of the Group III element oxide; and a crystal generation step of causing the gas of the reduced product and a nitrogen-containing gas to react with each other to generate the Group III element nitride crystal 12. The crystal growth plane is a plane on the −c-plane side. A crystal growth temperature is 1200° C. or more. In the vapor phase growth step, the Group III element nitride crystal is grown in an approximately −c direction.

Provided are a tabular alumina particle and a method for manufacturing it, wherein the particle has a major axis of 30 μm or more, a thickness of 3 μm or more, and an aspect ratio of 2 to 50 and contains molybdenum; and the method includes the steps of mixing an aluminum compound of 10% by mass or more in a form of Al.sub.2O.sub.3, a molybdenum compound of 20% by mass or more in a form of MoO.sub.3, a potassium compound of 1% by mass or more in a form of K.sub.2O, and silicon or a silicon compound of less than 1% by mass in a form of SiO.sub.2, where total amount of raw materials is assumed to be 100% by mass in forms of oxides, so as to produce a mixture and firing the resulting mixture.

A production method for a group III nitride crystal, the production method includes: preparing a plurality of group III nitride pieces as a plurality of seed crystals on a substrate, and growing a group III nitride crystal by bringing a surface of each of the seed crystals into contact with a melt that comprises at least one group III element selected from gallium, aluminum, and indium, and an alkali metal in an atmosphere comprising nitrogen, and thereby reacting the group III element and the nitrogen in the melt, wherein the step of growing a group III nitride crystal includes: growing a plurality of first group III nitride crystals whose cross-sections each have a triangular shape or a trapezoidal shape, from the plurality of seed crystals; and growing second group III nitride crystals each in a gap among the plurality of first group III nitride crystals.

Heterogeneous monolithic crystals that can include multiple regimes in a complex geometry are described. The crystals can be advantageously utilized in laser applications. The heterogeneous crystals can be created through growth of different regimes in interior voids formed in a seed crystal, which can in turn be homogeneous or heterogeneous. In one particular embodiment, a regime can be grown within a void of a seed crystal by use of a hydrothermal growth process. Formed crystals can be utilized in lasing and waveguiding applications, among others.

To provide a method for producing a Group III element nitride crystal by growing it on a plane on the c-plane side as a crystal growth plane. The present invention is a method for producing a Group III element nitride crystal, including a vapor phase growth step of growing a Group III element nitride crystal 12 on a crystal growth plane of a Group III element nitride seed crystal 11 by vapor deposition. The vapor phase growth step is a step of causing a Group III metal, an oxidant, and a nitrogen-containing gas to react with one another to grow the Group III element nitride crystal 12 or includes: a reduced product gas generation step of causing a Group III element oxide and a reducing gas to react with each other to generate a gas of a reduced product of the Group III element oxide; and a crystal generation step of causing the gas of the reduced product and a nitrogen-containing gas to react with each other to generate the Group III element nitride crystal 12. The crystal growth plane is a plane on the c-plane side. A crystal growth temperature is 1200 C. or more. In the vapor phase growth step, the Group III element nitride crystal is grown in an approximately c direction.

To provide a method for producing a Group III element nitride crystal by growing it on a plane on the c-plane side as a crystal growth plane. The present invention is a method for producing a Group III element nitride crystal, including a vapor phase growth step of growing a Group III element nitride crystal 12 on a crystal growth plane of a Group III element nitride seed crystal 11 by vapor deposition. The vapor phase growth step is a step of causing a Group III metal, an oxidant, and a nitrogen-containing gas to react with one another to grow the Group III element nitride crystal 12 or includes: a reduced product gas generation step of causing a Group III element oxide and a reducing gas to react with each other to generate a gas of a reduced product of the Group III element oxide; and a crystal generation step of causing the gas of the reduced product and a nitrogen-containing gas to react with each other to generate the Group III element nitride crystal 12. The crystal growth plane is a plane on the c-plane side. A crystal growth temperature is 1200 C. or more. In the vapor phase growth step, the Group III element nitride crystal is grown in an approximately c direction.