Novel ternary layered manganese bismuth tellurides of the MnTe-Bi2Te3 system: Synthesis and crystal structure

It is shown that MnTe-Bi2Te3 system is quasi-binary and in fact hosts three intermediate phases. Along with already known MnBi2Te4 phase, another two, MnBi4Te7 and MnBi6Te10 have been found to exist. All the phases melt incongruently in a very narrow temperature range of 577e590 C via peritectic reactions. Directional crystal growth results in hetero-phase ingots due to the narrow compositional range and narrow primary crystallization fields. The crystal structure of each phase is a derivation of the prototype tetradymit-type layered structure and the phases constitute a new homologous series with the chemical formula (MnTe)$n(Bi2Te3). X-ray diffraction patterns and Raman spectroscopy of the sorted-out single phase samples show that different phases have different number of the seven (7)- and five (5)-layer blocks and their different stacking manner in the unit cell. In particular, MnBi2Te4 exhibits the -7-7-7-, MnBi4Te7 -5-7-5-7-, and MnBi6Te10 -5-5-7-5-5-7- sequence of the blocks. Thus, these structures are the first derivatives of Bi2Te3 structure to contain a transition metal cation Mn2þ .