Lattice Collapse and Spin-state Transition in Manganese Chalcogenides

Figure caption: Experimental data of unit cell volume (left) and Mn K<sub>β1</sub>,3 x-ray emission spectra (right) of MnS as a function of pressure.
Figure caption: Experimental data of unit cell volume (left) and Mn Kβ1,3 x-ray emission spectra (right) of MnS as a function of pressure.

A phase transition with an abrupt volume collapse of >20% could be associated with dramatic changes of electronic orbitals and/or spin-states of involved transition metals. Using HPCAT capabilities of high-pressure X-ray diffraction and X-ray emission spectroscopy, the mechanism of the pressure-driven lattice collapse in MnS and MnSe is studied. Both MnS and MnSe exhibit a rocksalt-to-MnP phase transition under compression with ~22-23% unit-cell volume changes at a similar pressure range around 25GPa. The phase transition was found to be coupled with the Mn2+(d5) spin-state transition from S=5/2 to S=1/2 and the formation of Mn-Mn intermetallic bonding. The mutual relationship between pressure-driven lattice collapse and the orbital/spin-state of Mn2+ in manganese chalcogenides provides an insight toward the exploration of new metastable phases with exceptional functionalities. (Published in Wang, et al., Angew. Chem. Int. Ed., 55, 10350, 2016)