A pyramidal growth method for long-seed KDP-type crystal. In the growth method provided by the present invention, the lower end of the long-seed crystal is restricted by a lower tray, and the upper end is free to grow into a pyramidal. At the same time, the four prismatic faces at two directions of [100] and [010] can grow, avoiding growth stress problem during crystal growth, and all cut optical elements have high optical quality. Because the growth process is that four prismatic faces with highly similar growth environments grow at the same time and stirring is applied by blade-like stirring paddles during the crystal growth process, the cut optical elements have high optical uniformity.

A pyramidal growth method for long-seed KDP-type crystal. In the growth method provided by the present invention, the lower end of the long-seed crystal is restricted by a lower tray, and the upper end is free to grow into a pyramidal. At the same time, the four prismatic faces at two directions of [100] and [010] can grow, avoiding growth stress problem during crystal growth, and all cut optical elements have high optical quality. Because the growth process is that four prismatic faces with highly similar growth environments grow at the same time and stirring is applied by blade-like stirring paddles during the crystal growth process, the cut optical elements have high optical uniformity.

An example ferroelastic ceramic composition includes at least one compound having a relative chemical formula of A.sub.XB.sub.YC.sub.(1-X-Y)D. Element A, element B, and element C are independently selected from different members of the group consisting of yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Element D is selected from the group consisting of phosphate, niobate, and tungstate. X and Y are each equal to or greater than zero and less than one. X and Y are collective less than one.

A device for growing a flat single crystal from a seed in a crystallization solution. A support element has a support face; a blocking element comprising a blocking face, positioned at a predefined distance from the support face to block the growth of the single crystal in a direction perpendicular to the support face; a seed protection member, configured to protect the seed during a crystallization solution treatment phase and to free a growth zone positioned between the support face and the blocking face during a rotation of the support element; the blocking element comprises a holding member that cooperates with the protection member, the holding member being movable between a first position where it holds the protection member against the support face during the treatment phase and a second position where the holding member is separated from the protection member and participates in the formation of the blocking face.

A device for growing a flat single crystal from a seed in a crystallization solution. A support element has a support face; a blocking element comprising a blocking face, positioned at a predefined distance from the support face to block the growth of the single crystal in a direction perpendicular to the support face; a seed protection member, configured to protect the seed during a crystallization solution treatment phase and to free a growth zone positioned between the support face and the blocking face during a rotation of the support element; the blocking element comprises a holding member that cooperates with the protection member, the holding member being movable between a first position where it holds the protection member against the support face during the treatment phase and a second position where the holding member is separated from the protection member and participates in the formation of the blocking face.

The present invention relates to compounds and their nonlinear optical (NLO) crystals of A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs), their producing method and uses thereof. A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) belong to triclinic crystal system, and have a space group of P1, crystal cell parameters of a=6.284(8)-8.784(3) , b=6.338(3)-8.838(3) , c=6.463(3)-8.963(3) , =70-105, =75-106, =76-107 and Z=1 and a unit cell volume of V=257.4(3)-696.0(6) .sup.3. A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) compounds were prepared by a high-temperature solid-state reaction method or a hydrothermal method, and A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) NLO crystals were prepared by a high-temperature solid-state reaction method, a hydrothermal method or a solution method. These materials can be used to manufacture second harmonic generator, up-down frequency converter, optical parametric oscillator, etc.

The present invention relates to compounds and their nonlinear optical (NLO) crystals of A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs), their producing method and uses thereof. A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) belong to triclinic crystal system, and have a space group of P1, crystal cell parameters of a=6.284(8)-8.784(3) , b=6.338(3)-8.838(3) , c=6.463(3)-8.963(3) , =70-105, =75-106, =76-107 and Z=1 and a unit cell volume of V=257.4(3)-696.0(6) .sup.3. A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) compounds were prepared by a high-temperature solid-state reaction method or a hydrothermal method, and A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) NLO crystals were prepared by a high-temperature solid-state reaction method, a hydrothermal method or a solution method. These materials can be used to manufacture second harmonic generator, up-down frequency converter, optical parametric oscillator, etc.

A method of producing an apatite crystal includes the steps of preparing an apatite single crystal expressed by the general formula M.sup.2.sub.5(PO.sub.4).sub.3X (M.sup.2 being at least atomic element selected from the group consisting of divalent alkaline-earth metals and Eu, and X is at least one atomic selected from the group consisting of halogens); placing the apatite single crystal into a space controllable to a predetermined atmosphere; supplying water vapor into the space; and heating such that the atmosphere in the space is within a 1000 C. to 1400 C. range.

A method of producing an apatite crystal includes the steps of preparing an apatite single crystal expressed by the general formula M.sup.2.sub.5(PO.sub.4).sub.3X (M.sup.2 being at least atomic element selected from the group consisting of divalent alkaline-earth metals and Eu, and X is at least one atomic selected from the group consisting of halogens); placing the apatite single crystal into a space controllable to a predetermined atmosphere; supplying water vapor into the space; and heating such that the atmosphere in the space is within a 1000 C. to 1400 C. range.

Method for limiting growth of KDP-type crystals with a long seed where an upper and a lower ends of the long seed crystal are respectively limited by an upper baffle plate and a lower tray to restrain growth of a pyramidal surface and allow only four prismatic surfaces in [100] and [010] directions to grow. Finally grown crystal contains no pyramid-prism interface that severely restricts quality of optical element, and all cut optical elements have high optical quality. As four prismatic surfaces are subjected to highly similar growing environment and grow simultaneously, all optical elements cut therefrom have high optical uniformity. Due to uniqueness of a cutting angle of a KDP crystal frequency-tripled element, high cutting efficiency is achieved in the element, and an area of a maximum frequency-tripled element that may be cut is known in advance according to a horizontal size of the grown crystal.