Abstract: A method of obtaining a crystal by crystal growth in the liquid phase from a seed in the form of a plate taken from a primary crystal, which method comprises at least two steps constituted firstly by forming first crystal growth to obtain a secondary crystal from a first seed taken from said primary crystal in a first growth zone, and secondly in performing second crystal growth from a second seed taken from said secondary crystal in a second growth zone, said first and second seeds being selected so that few of the dislocations that they contain propagate respectively into the second zone of the secondary crystal or into the first growth zone of the resulting crystal. According to the invention said first and second crystal growth steps are performed in different growth directions. Application to monocrystals of quartz, or of materials that are isomorphs of quartz, such as berlinite, and that are intended for use in making electronic components, in particular oscillators and filters.

Abstract: The invention relates to a process for the preparation of berlinite crystals AlPO.sub.4, with a high Q factor, from seeds or crystalline flakes of AlPO.sub.4, by a hydrothermal method. It is characterized in that the crystallization solution is a sulfuric solution of AlPO.sub.4. The invention also relates to the berlinite monocrystals obtained by this process.