Solving Mysteries and Outwitting Transitions : Investigating the Incommensurate Crystal Structures of AuIn and Sn3Sb2

Sammanfattning: This thesis introduces two new incommensurate alloys. AuIn shows variable amounts of modulation, depending on the measurement temperature. At 400°C the diffraction pattern shows diffuse scattering and a thallium iodide type Cmcm space group. The diffuse scattering condenses into first order satellites on cooling to 300°C and the space group transforms to the incommensurate C-1(α, β, γ)0. I.e. the structure is becoming more ordered. If the measurement temperature is lowered even further to room temperature, satellites up to third order can be found. However the space group and the network structure do not change. The second alloy Sn3Sb2 is a high temperature modification of stistaite, SnSb. It can only be accessed when a pre-grown crystal is mounted in a capillary, with an additional piece of tin and heated to a temperature of 250°C. This way a structure made of 7x7x7 NaCl-type clusters interleaved with single layers of Sn with the space group Xm-3m can be found. If only the pre-grown crystal is measured, be it room or elevated temperatures, the diffraction pattern shows a twinned SnSb structure, with parasitic $\beta$-Sn reflections. In the future, further structures that crystallize in the TlI structure will be investigated, to see if they behave similar to AuIn.