The influence of X-ray radiation damage on the incommensurate phase in (N(CH₃)₄)₂ZnCl₄

Abstract

The modulated phase in tetramethylammonium zinc chloride was investigated by means of X-ray diffraction. The authors have determined its properties in a sample obtained in a gel, which is of very high quality. The thermal variation of the modulation wavenumber qdelta is practically free of global hysteresis. X-ray radiation damage caused by a strong-intensity beam (40 kV, 13 mA) induces dramatic changes in these features: the global hysteresis is progressively enhanced, up to the incommensurate transition temperature, and qdelta varies by jumps in the sample irradiated for 4 h. The intensity, position and width of the satellite are measured. The results are interpreted on the basis of pinning phenomena and of deperiodisation defects which have previously been described by other authors.