Ten Layered Hexagonal Perovskite Sr₅Ru_5−xO₁₅ (x = 0.90), a Weak Ferromagnet with a Giant Coercive Field H_c ∼ 12 T

A single crystal of Sr5Ru5−xO15 (x = 0.90(2)) with mixed valence of Ru(IV) and Ru(V) was synthesized under a high pressure of 4 GPa with an oxidizer. Sr5Ru5−xO15 crystallizes in a hexagonal perovskite-type structure with a space group P63/mmc (No.194), a = 5.5600(11) A, and c = 22.830(5) A. An alternative stacking of four corner-sharing (c) SrO3 layers and one face-sharing (h) SrO3 layer linking RuO6 octahedra and its doubling along c-axis gives a 10 layer period hexagonal cell (10H) which is denoted by (cccch)2. The partial deficiency of Ru found in face-sharing octahedra, as reported for 8H-Sr4Ru4−xO12 (x = 0.95) with (ccch)2 stacking, yields an average Ru valence estimate of 4.87. The bond valence analysis indicates that the valence of Ru in fully corner-sharing octahedra is nearly 5, while that of Ru in face-sharing octahedra is considerably lower than 5. This compound is a weakly ferromagnetic metal with Curie temperature Tc = 160 K and a saturated moment of 0.07 and 0.05 μB/Ru in H ⊥ c and H // c, r...