Symmetry-Breaking Transitions from GdCuAs2 through GdCuAs1.15P0.85 to GdCuP2.20: Crystal Structure, Application of Landau Theory, Bonding, Magnetic and Electrical Properties

The crystal structures of GdCuAs2, GdCuAs1.15P0.85, and GdCuP2.20 have been investigated by the single crystal and powder methods. While GdCuAs2 (P4/nmm) retains the tetragonal HfCuSi2 structure (M. Brylak, M. H. Möller, and W. Jeitschko, J. Solid State Chem. 115, 305 (1995)), GdCuAs1.15P0.85 (Pmmn, a=3.849(1), b=3.8501(1), c=9.871(3) Å) and GdCuP2.20 (Pmm2, a=5.3747(9), b=5.3830(9), c=9.7376(16) Å) undergo orthorhombic distortions. The changes …