Single‐Crystal X‐ray Diffraction and Electron Microprobe Analysis of the Structurally related J‐Phases Nd₄[Si₂O₅N₂]O₂, Nd₄[Si_2−xAl_xO_5+xN_2−x]O₂ with x ≈ 0.4 and Sr_xHo_4−x[Si_2−yAl_yO_5+(x+y)N_2−(x+y)]O₂ with x ≈ 0.2 and y ≈ 0.4

Abstract

Abstract The oxonitridosilicate Nd 4 [Si 2 O 5 N 2 ]O 2 , and the oxonitridoaluminosilicates Nd 4 [Si 2−x Al x O 5+x N 2−x ]O 2 with x ≈ 0.4 and Sr x Ho 4−x [Si 2−y Al y O 5+(x+y) N 2−(x+y) ]O 2 with x ≈ 0.2 and y ≈ 0.4 were obtained by the reaction of the lanthanide metals, silicon diimide “Si(NH) 2 ” and additional SiO 2 , AlN and SrCO 3 , respectively. The reactions were performed in a radio‐frequency furnace at temperatures between 1800 and 2100 °C. The crystal structures of the three compounds were determined by single‐crystal X‐ray diffraction ( P 2 1 / c , no. 14, Z = 4; Nd 4 [Si 2 O 5 N 2 ]O 2 : a = 7.8577(8) Å, b = 10.7793(12) Å, c = 11.0163(12) Å, β = 110.759(11)°, R 1 = 0.0752; Nd 4 [Si 2−x Al x O 5+x N 2−x ]O 2 : a = 7.842(2) Å, b = 10.710(2) Å, c = 11.074(2) Å, β = 110.32(3)°, R 1 = 0.1078; Sr x Ho 4−x [Si 2−y Al y O 5+(x+y) N 2−(x+y) ]O 2 : a = 7.5704(5) Å, b = 10.4744(8) Å, c = 10.8502(11) Å, β = 109.856(7)°, R 1 = 0.0825). The compound Sr x Ho 4−x [Si 2−y Al y O 5+(x+y) N 2−(x+y) ]O 2 crystallizes isotypically with the mineral cuspidine (Ca 4 [Si 2 O 7 ]F 2 ), the neodymium compounds crystallize in a cuspidine‐related structure type. The structure refinements were performed utilizing an O/N distribution model according to Paulings rules and according to powder neutron diffraction data obtained from La 4 Si 2 O 7 N 2 and Lu 4 Si 2 O 7 N 2 by Takahashi et al., i.e. nitrogen was positioned on the bridging site, mixed O/N‐occupation was assumed on the terminal sites and oxygen was positioned on the isolated site resulting in charge neutrality of the compounds. The Si and Al atoms were refined equally mixed on the two possible positions. The structures consist of bitetrahedral units [(Si,Al) 2 (O,N) 7 ], lanthanide and alkaline earth cations and isolated oxygen anions. The chemical compositions of all three compounds were determined by electron probe micro analyses (EPMA).