Abstract: | Crystal structures of the compounds SmCu1+δAs2—χPχ (δ = 0 — 0.2, χ = 0 — 2) undergoing symmetry‐breaking transitions and SmCuP2.3 have been investigated by the X‐ray single crystal and powder methods. While the phases SmCuAs2 through SmCuAs1.22P0.78 retain the tetragonal HfCuSi2 structure (P4/nmm space group), the compounds SmCuAs1.11P0.89 through SmCuAs0.56P1.44 adopt the GdCuAs1.15P0.85—type structure (Pmmn space group), an orthorhombic variant of the HfCuSi2‐type. Further distortion follows in SmCuAs0.33P1.67 through SmCuP2.3, the powder patterns of which were indexed in the P2/n space group (P2/c in a standard setting). According to Landau theory the transitions from tetragonal SmCuAs1.22P0.78 to orthorhombic SmCuAs1.11P0.89 and from orthorhombic SmCuAs0.56P1.44 to monoclinic SmCuAs0.33P1.67 can be continuous. Introducing extra copper into some of the orthorhombic arsenophosphides restabilizes tetragonal phases (0 < δ ≤ 0.2) with the P4/nmm symmetry, and the reverse transition Pmmn → P4/nmmcan be continuous. Inserting copper atoms into monoclinic SmCuP2 yields the SmCu1+δP2 phosphides with Cmmm symmetry, and this transition is first‐order. Single crystals of SmCu1.05As1.67P0.33, SmCu1.07As0.85P1.15 and SmCu1.15P2 have been prepared using iodine as a mineralizing agent. Their structures have partially occupied Cu sites around the square As/P or P layers and they are a stuffed variant of the HfCuSi2 structure for SmCu1.05As1.67P0.33 (P4/nmm, a = 3.9163(6), c = 9.932(2)Å), a stuffed GdCuAs1.15P0.85 structure for SmCu1.07As0.85P1.15 (Pmmn, a = 3.859(1), b = 3.862(1), c = 9.852(3)Å) and a CeCu1.12P1.97‐type structure for SmCu1.15P2 (Cmmm, a = 5.453(3), b = 19.511(10), c = 5.439(3)Å). The P net in SmCu1.15P2 is broken into rectangular units. The results of magnetic measurements for SmCuAsP are reported. |