Structure of the modulation in thiourea. II. Structure refinement
نویسندگان
چکیده
2014 We describe structure refinement of the long-period, commensurate, q = b*/9 phase of thiourea, using neutron diffraction data and the model derived in a previous paper. The primary distorsion wave and two harmonics are taken into account and fitted to 660 fundamental and satellite reflections. The displacive modulation is mainly a sinusoidal rotation around the b axis (Rb = 0.116 rad) and a sinusoidal translation along c (T = 0.03 c), with small longitudinal and non-sinusoidal components. Amplitudes of harmonics two and three are |Q3q| ~ |Qq| /10 ; |Qq| /100 ~ |Q2q| |Qq| /10. An order-disorder model does not fit the data. Information derived from the Landau free energy is compared to the superspace group approach. J. Phys. France 49 (1988) 471-480 MARS 1988, Classification Physics Abstracts 61.12 61.50E 64.70 63.75
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Structure of the modulation in thiourea. I. symmetry properties
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تاریخ انتشار 2017