The thermal behaviour of TKX-50 was reinvestigated in an extended temperature range by means of temperature resolved X-ray diffraction. TKX-50, synthesized at the Fraunhofer ICT, was identified using Rietveld-analysis and reference data from the CCDC. Monitoring the refined crystal data versus temperature verified a highly anisotropic expansion behavior connected to a layer structure. However, the coefficients of thermal expansion (CTEs) were found at an order of magnitude higher than reported, and a slight bent of lattice parameter a was found near room temperature. At temperatures between 180 and 200 degrees C the decomposition of TKX-50 started with the formation of 1 to 5 wt.% diammonium 5,5'-bistetrazole-1,1'-diolate (ABTOX). Moreover, the micro structure was investigated by means of size/strain analysis and so called indexed Williamson-Hall plot. The analysis revealed moderate micro strain and absence of size broadening. The results give rise to the hypothesis that the (010) layer structure supports a low sensitivity of TKX-50 without impairment of the mechanical stability. The results provide a base for future quality assessment and the development of advanced products.