Abstract
The aspects of structure, dipole ordering, and ionic conductivity of the Na 3 Cr 2 (PO 4 ) 3 crystal with the four polymorphic phases (α, α', β, and γ) have been investigated. The features of the α-Na 3 Cr 2 (PO 4 ) 3 crystal structure and its dipole ordering and relaxation polarization in the low-temperature α and α' phases have been refined. The occurrence of Na 3 Cr 2 (PO 4 ) 3 dipole ordering in the α and α' phases and high ionic conductivity in the β and γ phases is attributed to the structural changes in the rhombohedral [ Me 2 (PO 4 ) 3 ] –3 3∞ crystal frame upon phase transformations α → α', α' → β, and β → γ. A model for explaining the dipole ordering and ionic conductivity phenomena in Na 3 Cr 2 (PO 4 ) 3 is proposed.