Method for growing single crystals of thermally unstable ferroelectric materials

Claim 1

A method for growing a single crystal of a ferroelectric material selected from the group consisting of ferroelectric materials having the formula MH 2 XO 4 , where M is rubidium, cesium or ammonium; H is hydrogen or deuterium and X is phosphorus or arsenic, said method comprising the steps of: providing a sealed vessel which defines a constant volume cylindrical chamber having a top end, side walls and a bottom end, said chamber being substantially full of said ferroelectric material and moisture-free, said chamber having an axis extending longitudinally from the chamber top end to the chamber bottom end; uniformly heating said ferroelectric material in said chamber to a sufficient temperature to uniformly melt said material only and not decompose said material; providing a seed or nucleation point at the end where crystal growth is initiated; and axially cooling said material to form a single solid crystal, said axial cooling being accomplished from the bottom end of said chamber by thermal conduction along the chamber axis predominantly and only minimally by radial thermal conduction through the vessel side walls, said axial cooling producing a crystal interface between said solid crystal material and melted material which is flat and perpendicular to said chamber axis, said crystal interface progressing from said chamber bottom end to said chamber top end due to said axial cooling to thereby provide uniform growth of said single crystal from the bottom end to the top end of said chamber.

Claim 2

A method for growing a single crystal of a ferroelectric material selected from the group consisting of ferroelectric materials having the formula MH 2 XO 4 , where M is rubidium, cesium or ammonium; H is hydrogen or deuterium and X is phosphorus or arsenic, said method comprising the steps of: providing a sealed vessel which defines a constant volume cylindrical chamber having a top end, side walls and a bottom end, said chamber being substantially full of said ferroelectric material and moisture-free, said chamber having an axis extending longitudinally from the chamber top end to the chamber bottom end; uniformly heating said ferroelectric material in said chamber to a sufficient temperature to uniformly melt said material only and not decompose said material; providing a seed or nucleation point at the end where crystal growth is initiated; and axially cooling said material to form a single solid crystal, said axial cooling being accomplished from the bottom end of said chamber by thermal conduction along the chamber axis predominantly and only minimally by radial thermal conduction through the vessel side walls, said axial cooling producing a crystal interface between said solid crystal material and melted material which is flat and perpendicular to said chamber axis, said crystal interface progressing from said chamber bottom end to said chamber top end due to said axial cooling to thereby provide uniform growth of said single crystal from the bottom end to the top end of said chamber.

Claim 13

A method for growing a single crystal of KH 2 XO 4 wherein H is hydrogen or deuterium and X is phosphorus, said method comprising the steps of: providing a sealed vessel which defines a constant volume cylindrical chamber having a top end, side walls and a bottom end, said chamber from about one-sixth to about one-third full of said KH 2 XO 4 and moisture-free, said chamber having an axis extending longitudinally from the chamber top end to the chamber bottom end; uniformly heating said KH 2 XO 4 in said chamber to a sufficient temperature to uniformly melt said material only and not decompose said material; providing a seed or nucleation point at the end where crystal growth is initiated; and axially cooling said material to form a single solid crystal, said axial cooling being accomplished from the bottom end of said chamber by thermal conduction along the chamber axis predominantly and only minimally by radial thermal conduction through the vessel side walls, said axial cooling producing a crystal interface between said solid crystal material and melted material which is flat and perpendicular to said chamber axis, said crystal interface progressing from said chamber bottom end to said chamber top end due to said axial cooling at a rate from about 0.1 mm to about 0.7 mm per hour to thereby provide uniform growth of said single crystal from the bottom end to the top end of said chamber.

Claim 14

A method for growing a single crystal of KH 2 XO 4 wherein H is hydrogen or deuterium and X is phosphorus, said method comprising the steps of: providing a sealed vessel which defines a constant volume cylindrical chamber having a top end, side walls and a bottom end, said chamber from about one-sixth to about one-third full of said KH 2 XO 4 and moisture-free, said chamber having an axis extending longitudinally from the chamber top end to the chamber bottom end; uniformly heating said KH 2 XO 4 in said chamber to a sufficient temperature to uniformly melt said material only and not decompose said material; providing a seed or nucleation point at the end where crystal growth is initiated; and axially cooling said material to form a single solid crystal, said axial cooling being accomplished from the bottom end of said chamber by thermal conduction along the chamber axis predominantly and only minimally by radial thermal conduction through the vessel side walls, said axial cooling producing a crystal interface between said solid crystal material and melted material which is flat and perpendicular to said chamber axis, said crystal interface progressing from said chamber bottom end to said chamber top end due to said axial cooling at a rate from about 0.1 mm to about 0.7 mm per hour to thereby provide uniform growth of said single crystal from the bottom end to the top end of said chamber.