Crystal structure and Raman active lattice vibrations of magnetic topological insulators MnBi2Te4 n(Bi2Te3) (n = 0, 1, . . . , 6)

TL;DR

This study investigates the crystal structure and Raman vibrational properties of MnBi2Te4 n(Bi2Te3) compounds with n=4 to 6, revealing their cubic close packing and dominant lattice dynamics within quintuple blocks.

Contribution

It provides new structural data for n=4, 5, 6 members and analyzes their Raman spectra, highlighting the dominance of quintuple block displacements in lattice vibrations.

Findings

All members follow cubic close packing regardless of space group.

Raman spectra show vibrational modes mainly involve quintuple block displacements.

Structural and vibrational data extend understanding of magnetic topological insulators.

Abstract

Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with n<4, where index n is the number of quintuple Te-Bi-Te-Bi-Te building blocks inserted between the neighboring septuple Te-Bi-Te-Mn-Te-Bi-Te building blocks, the structure of the members with n=4, 5 and 6 was studied using X-ray powder diffraction. The unit cell parameters and atomic positions were calculated. The obtained and available structural data were summarized to show that the crystal structure of all members of MnBi2Te4 n(Bi2Te3) follows the cubic close packing principle, independently of the space group of the given member. Confocal Raman spectroscopy was then applied. Comparative analysis of the number, frequency, symmetry, and broadening of the vibration modes responsible for the lines in the Raman spectra of the systems with n=1,. . . ,6, as well as MnBi2Te4 (n=0) and Bi2Te3 (n=infinity) has shown that lattice dynamics of MnBi2Te4 n(Bi2Te3) with n>0 overwhelmingly dominates by the cooperative atomic displacements in the quintuple building blocks.