Observations of growth defects in berlinite by high-temperature X-ray topography

Abstract

Growth defects in a synthetic berlinite sample were studied at high temperature (300--500 K) by X-ray topography. Preliminary observations of contrast changes with temperature are reported.During the past few years there has been a resurgence of interest in berlinite (AIPO4) as a possible substitute for quartz in piezoelectric device applications. Berlinite has a similar structure (Schwarzenbach, 1966) to quartz at room temperature (RT) and at higher temperature exhibits the same type of polymorphism. In particular, A1PO4 shows an ~-fl transition occurring at 853 K instead of 846 K for quartz (Van Tendeloo, Van Larduyt & Amelinckx, 1976;Bachheimer, Berge, Dolino, Saint-Gregoire & Zeyen, 1984). In evaluating berlinite as a replacement for quartz in highfrequency acoustic-wave devices, anomalies were observed in its propagation loss-frequency-temperature characteristics (Detaint, Poignant & Toudic, 1980;Steinberg, Roy, Estes, Chai & Morris, 1984). In an attempt to explain these electrical anomalies, we shall present in this paper some results concerning the defects in a berlinite sample observed by X-ray topography above RT.(a) (b) (c) (d) (e) Fig. l(a).

Observation of defects and the incommensurate phase in berlinite crystals by high-temperature X-ray topography

“…The role of the temperature is to create locally or in the whole crystal defects like dislocation loops (Doukhan & Trepied, 1985) or bubbles whose number and dimensions can sometimes, when annealing is important, bleach the whole crystal. Contrary to previous results (Zarka & Capelle, 1985) these changes of contrast started at about 360K and increased with temperature. Moreover, strong contrast is present in the incommensurate phase as well as in the a (Fig.…”

“…3(b). As in another case previously studied between RT and 423K (Zarka & Capelle, 1985) it seems that these features are directly due to the high water content in this crystal. The role of the temperature is to create locally or in the whole crystal defects like dislocation loops (Doukhan & Trepied, 1985) or bubbles whose number and dimensions can sometimes, when annealing is important, bleach the whole crystal.…”