SrPd₄B and BaPd₄B: new type of crystal structure and physical properties

Two new intermetallic alkaline-earth palladium borides, SrPd₄B and BaPd₄B were synthesised and their physical properties were investigated. The crystal structure of SrPd₄B was solved from powder X-ray diffraction data: new structure type, space group Pnma, a = 6.0014(1) Aa, b = 5.5041(1) Aa, c = 11.8723(2) Aa, R_I = 0.065, R_P = 0.093. BaPd₄B is isostructural with a = 6.0883(1) Aa, b = 5.6066(1) Aa, c = 12.0050(2) Aa, R_I = 0.062, R_P = 0.097. The relationship of this structure type with the series of derivatives of the CaCu₅ type is discussed. Calculated electronic band structures for palladium, Pd₃B, SrPd₅, SrPd₄B and SrPd₃B are compared. The role of boron and strontium for the electronic properties is discussed in detail. SrPd₄B shows metallic behaviour with a DOS(E_F) ∼ 1.7 eV^-1.f.u.^-1 at the Fermi level. Magnetic properties, electrical resistivity and specific heat capacity measurements reveal that the two compounds are diamagnetic metallic conductors with low electronic density of states, in agreement, with the electronic structure calculations. (Abstract Copyright [2010], Wiley Periodicals, Inc.)