Lithium-cation conductivity and crystal structure of lithium diphosphate

The electrical conductivity of lithium diphosphate Li4P2O7 has been measured and jump-like increasing of ionic conductivity at 913K has been found. The crystal structure of Li4P2O7 has been refined using high temperature neutron diffraction at 300–1050K. At 913K low temperature triclinic form of Li4P2O7 transforms into high temperature monoclinic one, space group P21/n, a=8.8261(4)Å, b=5.2028(4)Å, c=13.3119(2)Å, β=104.372(6)°. The migration maps of Li+ cations based on experimental data implemented into program package TOPOS have been explored. It was found that lithium cations in both low- and high temperature forms of Li4P2O7 migrate in three dimensions. Cross sections of the migrations channels extend as the temperature rises, but at the phase transition point have a sharp growth showing a strong “crystal structure – ion conductivity” correlation. Crystal structure of Li4P2O7 at 950K. Red balls represent oxygen atoms; black lines show Li+ ion migration channels in the layers perpendicular to [001] direction. [Display omitted] •Structure of Li4P2O7 has been refined using high temperature neutron diffraction.•At 913K triclinic form of Li4P2O7 transforms into high temperature monoclinic one.•The migration maps of Li+ implemented into program package TOPOS have been explored.•Cross sections of the migrations channels at the phase transition have a sharp growth.