What is it about?
Two-dimensional modulation in Akermanite-type compounds Ca2MgSi2O7 and Ca2ZnSi2O7 has been studied by the single-crystal X-ray diffraction methods in the temperature range between 18 and 297 K. It is found that change of the modulation wavelength Ca2MgSi2O7 is slight, but that inCa2ZnSi2O7 it is noticeable and indicates a plateau-like temperature dependence. The plateau-like region may be regarded as an independent phase.
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Why is it important?
Akermanite-type compounds, Ca2MgSi2O7 and Ca2ZnSi2O7,exhibit two-dimensional structural modulations. The incommensurate-to-normal phase transition occurs in Ca2MgSi2O7 at Ti=355K and in Ca2ZnSi2O7 at Ti = 405 K. Although the peculiarities of this phase transition in modulated akermanites have been well studied, the structural data at low temperatures are few.
Perspectives
Because incommensurate modulations are observed in many compounds as intermediate states between high-temperature normal and low-temperature commensurate phases and the modulation in akermanites, being two-dimensional,is a unique one,it is of interest to study the transformations of the modulated structures in Ca2MgSi2O7 and Ca2ZnSi2O7 at low temperature. In general, a lock-in phase transition causes positional shift of satellites to commensurate positions and an increase in their intensity. We present precise X-ray diffraction studies of the Ca2MgSi2O7 and Ca2ZnSi2O7 crystals over a wide temperature range, 18–297 K.
Dr Bagautdin Bagautdinov
Read the Original
This page is a summary of: Low-temperature studies on the two-dimensional modulations in åkermanite-type crystals: Ca 2 MgSi 2 O 7 and Ca 2 ZnSi 2 O 7, Physics and Chemistry of Minerals, June 2002, Springer Science + Business Media,
DOI: 10.1007/s00269-002-0238-6.
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