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 present invention relates to a process for increasing the dimensions of quartz crystals and of quartz-isomorphic materials, which can be produced by hydrothermal growth from seed, in which a seed obtained by assembly of several crystalline plates is used, wherein there are assembled at least two plates of strictly identical lengths and/or widths and of similar thicknesses, cut in at least one crystal and having, on at least three faces crystalline orientations, the deviations from which remain, between the plates, smaller than about 10" of arc, and wherein said plates are brought together on a support by guidance elements, thus ensuring their alignment on the aforementioned three faces while maintaining crystalline orientation deviations smaller than about 10" of arc, one face per plate being left free for growth of the assembled seeds, leading to the production of a single crystal exhibiting at least one dimension greater than that corresponding to the original crystalline plate.

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.

Abstract: The present invention relates to a process for the preparation of mono-crystalline 3-5 semi-insulating materails by doping, characterized in that the starting charge of type .rho. is doped with at least one deep donor due to a transition element. It relates also to the use of the semi-insulating materials obtained in the fields of optoelectronics and of rapid electronics.