Phasons modulate the atomic Debye–Waller factors in incommensurate structures: experimental evidence in ThBr4 at 55 K

Abstract

The incommensurate displacive structure of β-ThBrg at 55 K has been determined from a neutron diffraction data set including main reflections and firstorder satellites. The superspace group is P s1s1 I41/amd . Final agreement factors are 0.0193, 0.0186 and 0.045 for all, main and satellite reflections, respectively. It is shown that the effect of phasons on the atomic Debye-Waller factors can be quantified by two additional structural parameters: the modulus β Br 11,2 and the phase χ Br 11,2 of a second harmonic that spatially modulates the temperature factors of Br atoms