Refinement of the composition and structure of YBaCo4−x Al x O7+δ crystals

Orthorhombic YBaCo4O8.4 crystals as a result of saturation of hexagonal YBaCo4O7 crystals with oxygen

“…Growth of cobaltate crystals in corundum crucibles leads generally to the considerable replacement of cobalt with aluminum (up to ~0.5 atoms per formula unit), which enters a growing crystal due to the interaction of melt with the container material [13]. This circumstance significantly affects the behavior of crystals during their saturation with oxygen.…”

“…Valldor [1] was the first to study the physical properties and determine the crystal structure of cobaltates belonging to the R-Ba-Co-O system (R is a rare earth element or Y) with the element ratio Y : Ba : Co : O = 1 : 1 : 4 : (7 + x) [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. RBaCo 4 O 7 + x (R114) compounds continue to attract much attention due to the unusualness and great variety of their physical properties (ferro-and antiferromagnetism, catalytic activity, etc.).…”

“…Thus, this structure can also be considered wurtzite-like and two-packet, because layers in a packet, as well as packets with respect to each other, obey the two-layer closest packing law. The single-crystal structure was determined for R = Y [2,13,14], Dy [2], Ho [2], and Lu [2,3].…”

Synthesis and oxygenation behavior of RBaCo4O7 + δ (R = Y, Dy-Lu)

“…The microstructure and ele mental composition of the RBaCo 4 O 7 + δ samples were determined by scanning electron microscopy on a JEOL JSM 6460LV equipped with an Oxford Instru ments INCA Energy 350 energy dispersive X ray (EDX) spectrometer system. The extreme oxygen compositions were obtained by a procedure described elsewhere [16]: holding for two days in air or an inert gas (depending on R) at 490-500°С in order to obtain δ 0 and stepwise cooling from 490°С to room temperature (30 days) in order to maximize the oxygen content.…”

“…Rudina for her assistance in scanning electron microscopic examination of the samples. Elemental composition of Y114 ceramics before (points 1-5) and after (points 6-9) oxygenation (the devi ation from cobalt stoichiometry is related to specific fea tures of standardless EDX analysis [16]). …”