(La 3 Z x )Al and (Ce 3 Z x )Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites

The inverse cubic perovskites (La 3 O)Al, (La 3 N)Al, (Ce 3 O)Al, and (Ce 3 N)Al are reported together with the solid solution series (Ce 3 C 1–x N x )Al. The crystal structure of (La 3 N)Al is analyzed in detail based on single crystal X-ray diffraction data (space group Pm -3 m , 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 -Ce 3 Al. Indications for the existence of a cubic β -Ce 3 Al with Cu 3 Au structure type could not be derived from any experiment. All studied phases are metals, the Ce compounds contain the rare-earth metal in Ce(4 f 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 (La 3 C)Al is mainly prohibited by insufficient charge transfer between the metal species.