Polishing and etching langasite and quartz crystals

Langasite is a promising new piezoelectric material which is similar to quartz in its acoustic behavior. Little was known until recently about the methods needed to mechanically polish and chemically polish/etch this material. The results of polishing and etching experiments are described. Conventional quartz polishing methods, with polishing agents such as a rare earth slurry or ruby powder, did not produce well polished surfaces. Polishing with a colloidal silica suspension has produced the best results, Polishing quartz with colloidal silica was also investigated. Colloidal silica was found to be capable of producing defect-free polished quartz surfaces as well. Y-cut langasite surfaces which had been polished with the colloidal silica suspension were etched in a variety of etchants. The conventional quartz etchants destroyed the polished surfaces. Other etchants formed a coating on the surfaces. An etching process was found which was able to etch without leaving a film on the surfaces. When colloidal silica polished surfaces were etched deeply with this etchant subsequent to polishing, the etching did not degrade the polished surfaces. Similar results were obtained with polished quartz. After deep-etching colloidal silica polished quartz surfaces, the surfaces remained polished (except for the defects which were brought out by the etchant)