Lithium titanium phosphate, with general formula (LTP or LTPO), is another lithium-containing NASICON material in which TiO6 octahedra and PO4 tetrahedra are arranged in a rhombohedral unit cell. The LTP crystal structure is stable down to 100 K and is characterized by a small coefficient of thermal expansion. LTP shows low ionic conductivity at room temperature, around 10−6 S/cm; however, it can be effectively increased by elemental substitution with isovalent or aliovalent elements (Al, Cr, Ga, Fe, Sc, In, Lu, Y, La). The most common derivative of LTP is lithium aluminium titanium phosphate (LATP), whose general formula is . Ionic conductivity values as high as 1.9×10−3 S/cm can be achieved when the microstructure and the aluminium content (x = 0.3 - 0.5) are optimized. The increase of conductivity is attributed to the larger number of mobile lithium ions necessary to balance the extra electrical charge after Ti replacement by Al, together with a contraction of the c axis of the LATP unit cell.
