Synthesis, crystal structure and superconductivity of LaNiPO

Single crystals of LaNiPO were synthesized by reacting La, P and NiO at 1173 K in a tin flux under argon atmosphere. A phase analysis and crystal structure determination was carried out using X-ray powder and single crystal methods. The quaternary phosphide oxide crystallizes in the tetragonal ZrCuSiAs structure (P4/nmm, a = 404.53(1) pm, c = 810.54(3) pm, Z = 2), which is characterized by layers of edge-sharing [La4/4O]∞2 and [NiP4/4]∞2 tetrahedra alternating along [001]. LaNiPO is a Pauli paramagnetic metal at room temperature and becomes a type-II superconductor at TC = 4.3 K with an upper critical field Hc2 ≈ 320 mT at 1.8 K. Connections between the crystal chemistry and the occurrence of superconductivity in LaNiPO and related ThCr2Si2 type compounds are discussed.

Figure optionsDownload as PowerPoint slide