(La3 Z x)Al and (Ce3 Z x)Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites

Abstract

Abstract The inverse cubic perovskites (La3O)Al, (La3N)Al, (Ce3O)Al, and (Ce3N)Al are reported together with the solid solution series (Ce3C1–xNx)Al. The crystal structure of (La3N)Al is analyzed in detail based on single crystal X-ray diffraction data (space group Pm-3m, a = 509.04(1) pm, Z = 1, R gt(F) = 0.008, wR(F 2) = 0.018). Combined X-ray powder diffraction and thermal analysis studies on samples with various N and O contents indicate only small tolerance of the ternary compounds towards Z = N, O deficiency and small solubility of Z in hexa gonal α-Ce3Al. Indications for the existence of a cubic β-Ce3Al with Cu3Au structure type could not be derived from any experiment. All studied phases are metals, the Ce compounds contain the rare-earth metal in Ce(4f 1) states according to X-ray absorption spectroscopy and measurements of the magnetic susceptibilities. The Ce moments order antiferromagnetically with T N decreasing and scaling with increasing unit cell dimension of the compounds. Electronic band structure calculations reveal a trend to increased mixing of Z and La states on going from Z = O via N to C. Formation of a band gap even in the formally electronically balanced (La3C)Al is mainly prohibited by insufficient charge transfer between the metal species.