High Pressure Induced Insulator-to-Semimetal Transition through Intersite Charge Transfer in NaMn7O12

Abstract

Abstract:The pressure-dependent behaviour of NaMn 7 O 12 (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18 GPa, accompanied by a change in the compressibility of the system. On the other hand, the crystallographic determinations rule out a symmetry change to be at the origin of the transition, despite all the structural parameters pointing to a symmetrizing effect of pressure. Bond valence sum calculations indicate a charge transfer from the octahedrally coordinated manganese ions to the square planar ones, likely favouring the delocalization of the carriers.

Pressure-induced structural phase transition and suppression of Jahn-Teller distortion in the quadruple perovskite structure

“…Such a maximization of packing prevents further pressure-induced lattice distortions, thus freezing the lattice degrees of freedoma favorable situation for realizing a purely electronic pressure-induced insulatormetal transition with no participation of the lattice, as originally proposed by Mott [12]. A first high-pressure study on (NaMn 3 )Mn 4 O 12 corroborates the conjecture of the stability of the QP cubic Im phase up to 20 GPa [13].…”

“…This is a highly favorable situation indeed for realizing in a real system the long-sought pressure-induced insulator-metal transition originally proposed by Mott [11], where only the electronic degrees of freedom come into play. A first study on (NaMn 3 )Mn 4 O 12 corroborates the conjecture of the stability of the QP cubic Im3 phase up to 20 GPa [12].…”