High-pressure synthesis, structure and properties of new ternary pnictides La3TiX5 (X = P, As)

Abstract

Abstract The new ternary pnictides La3TiX5 (X = P, As) and the solid solutions of La3Ti(Sb1-xAsx)5 (x = 0–1) and La3Ti(As1-yPy)5 (y = 0–1) were synthesized under high pressure and high temperature conditions. The crystal structure of La3TiX5 (X = P, As) was determined from the X-ray powder diffraction data. These compounds crystallize in a hexagonal Hf5Sn3Cu-anti type structure with the space group P63/mcm and lattice parameters a = 8.7927 A and c = 5.7643 A for La3TiP5, and a = 9.0267 A and c = 5.9071 A for La3TiAs5, in which the face-sharing TiX6 octahedral chains running along the c axis are separated by La3+ in the interstice sites with a distance about 9 A, presenting a strong one-dimensional crystal structure. Physical properties measurements indicate La3TiX5 (X = P, As) are Pauli paramagnetic metals. The calculations reveal that La3+ ions are not perfectly ionic owing to the non-negligible contributions of La to the density of state (DOS) at the Fermi level and bridge the X atoms between the chains, which make the samples to be 3-dimensional metals. What’s more, the change of X in La3TiX5 from Sb to P increases the ionicity of La3+ and thus decreases the electron hopping between the conducting chains.