The synthesis, structure and properties of a new lithium-rich manganese(ii) phosphate Li5CsMn(P2O7)2: a congruently melting compound with a ‘lithium hamburger’ structure

Abstract

The crystals of the title compound have been grown in molten salt media. Single-crystal X-ray diffraction experiment revealed that the compound crystallizes in an orthorhombic space group Pbcn (no. 60) with cell parameters: a = 5.1023(10) Å, b = 19.717(4) Å, c = 12.557(3) Å, and Z = 4. The structure of Li₅CsMn(P₂O₇)₂ consists of one-dimensional manganese pyrophosphate chains [MnP₄O₁₄]_∞ interleaved with Cs⁺ and Li⁺ cations. A pseudo-two-dimensional layer [CsMnP₄O₁₄]_∞ parallel to the ab plane is made up of [MnP₄O₁₄]_∞ chains and Cs–O polyhedra through sharing the oxygen atoms. The three crystallographically distinct Li atoms are all located in the interlayered space to form a ‘lithium hamburger’ structure. Magnetic studies demonstrated that the compound shows paramagnetic behavior. DSC and XRD investigations revealed that the compound melts congruently. AC impedance studies show that the conductivity is 1.3 × 10⁻⁵ S cm⁻¹ at 573 K and the activation energy is 0.42 eV. In addition, Li ion diffusional pathways were obtained using the bond valence map.