Quaternary rare-earth transition-metal phosphides REMnCuP2 (RE = Y, La–Nd, Sm, Gd–Tm, Lu) with CaAl2Si2-type structure and a polymorph of LaMnCuP2 with BaCu2S2-type structure.

Abstract The series of quaternary rare-earth phosphides RE MnCuP 2 (RE = Y, La–Nd, Sm, Gd–Tm, Lu), which had previously been limited to the Yb member, has been prepared by reaction of the elements at 800 °C. These phosphides adopt the CaAl 2 Si 2 -type structure (trigonal, space group P 3 ¯ m 1 , Z = 1) with Mn and Cu atoms disordered over the tetrahedral M sites within [ M 2 P 2 ] slabs. However, single-crystal X-ray diffraction studies, carried out on some of these members (RE = Tb, Dy, Er, Tm), provide evidence for an interstitial octahedral site being partially occupied by Cu atoms, resulting in the nonstoichiometric formulation RE MnCu 1+ x P 2 (x = 0.10–0.16). A second polymorph of LaMnCuP 2 adopting the BaCu 2 S 2 -type structure (orthorhombic, space group Pnma , Z = 4) was also identified in the course of these investigations. Electronic structure calculations on a ordered superstructure model of YMnCuP 2 indicate the absence of a band gap. Graphical abstract RE MnCuP 2 with CaAl 2 Si 2 -type structure forms for nearly all RE members, and LaMnCuP 2 forms an additional BaCu 2 S 2 -type polymorph. fx1 Highlights • Phosphides RE MnCuP 2 with CaAl 2 Si 2 -type structure were prepared for nearly all RE. • Slight excess of Cu atoms can be accommodated in interstitial octahedral sites. • LaMnCuP 2 forms a second polymorph with BaCu 2 S 2 -type structure. • Calculations on YMnCuP 2 indicate absence of band gap. [ABSTRACT FROM AUTHOR]