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This paper presents a new method for obtaining electnc twins in quartz crystal: thermal treatment in a temperature gradient at about 500 "C, that means under phase transition point. + 5X quartz crystal plates for resonators were used; a temperature gradient of 15-25 "C was applied for 4-5 hours along the Y axis (the place length). For +5X resonators, the diminution of the resonant frequency and the increase of the inductance were plotted as a function of the level of twinning.Ce travail presente une nouvel methode de realiser un maclaje electrique dans les cristaux de quartz: le traitment thermique en gradient de temperature a 500 "C approximativement. On a utilii des plaquettes de quartz a coupure + 5X; le gradient de temperature de 15 -25 "C a ete applique au long de I'axe Y (longuere de la plaque). Pour les resonateurs + 5X, on a represente, par des grafics, la diminuation de la frequence de resonance ainsi que l'augmantation de I'inductence en fonction du niveau de maclaje.

In the present study the linear defects in several synthetic quartz have been surveyed by X-ray topography using Lang method. The grown-in dislocations produced by layers displacement around holes, precipitates or inclusions are discussed. Each growth zone is described with their own defects pattern and some correlations with the external morphology of the crystal are stated. There are also pointed out the asymmetry of the defects for every growth zone and the specific role in the growth mechanism of the s-growth zone. In the final part of the work there are outlined the general and the specific conclusions.Dans l'ktude prksente sont analiskes les defaults lineaires dans quelques quartz de synthese par topographie avec rayons X, la mkthode Lang. Ainsi, sont discutkes les dislocations produit par le deplacement des plans cristallins autour de nus, de precipitations ou d'inclusions. Chaque secteur de croissance est dkcrit ayant sa propre structure de defaults qui ont ses implications dans la morphologie extkrieur de cristal-I1 est met en kvidence l'asymetrie de defauts pour chaque secteur de croissance et en meme temp le r61e particulier de secteur de croissance s dans la mkcanisme de croissance. A la fin de l'etude sont prksentkes les conclusions genkrales et spkcifiques.

The paper presents two original methods for obtaining electrical twins up to the transition point in quartz crystal: a) thermal treatment in a temperature gradient of 10-1.5 degreekm at about 5OO0C and b) applying an electric field of 14kVkm at 50OoC. The twinning time dependence on the temperature, the dynarmc of twin domain formation as a function of directions. thickness. temperature gradient, for +SX resonator plates are discussed. The influence of the Dauphine tuins on the performances of piezoelectric resonators: resonant frequency. dynamic inductance and equivalent dynamic capacity was previously reported [I].This paper presents the influence of twinning area on the frequency spectrum of a resonator plate of + 5 X a t and the changing of the frequency-temperature characteristic urhen the resomtor plate becomes minned.

The present paper is a review of the data about the dislocations in the as-grown quartz crystal. The work presents some general considerations about dislocations, their origins and causes, methods of their observation and techniques to reduce the dislocations density. It is also shown a method to obtain a new shape crystal used in the positive X-seeds preparation.Ce travail est un passage en revue des dates sur les dislocations dans les cristaux syntetique de quartz. I1 presente quelques considerations gknerales sur les dislocations et leurs origine et causes de formation, des methodes qui permettent d'observer les dislocations ansi que des techniques pour reduire leur densitt-. On presente aussi une methode pour obtenir une nouvelle forme de cristal, forme utiliske d a m la preparation de germes X-positifs.