New phases induced by hydrogen reduction and by subsequent oxidation of L sub 2 CuO sub 4 ( L =La,Pr,Nd,Sm,Eu,Gd)
- Ames Laboratory-U.S. Department of Energy, Ames, IA (USA) Department ofPhysics, Iowa State University, Ames, IA (USA)
We report the synthesis of new compounds {ital L}{sub 2}CuO{sub 3.5} ({ital L}=Pr,Nd,Sm,Eu,Gd) and La{sub 2}CuO{sub 3.67}, obtained by heating conventionally prepared {ital L}{sub 2}CuO{sub 4} powders in a 5 mol % H{sub 2}/He atmosphere at low temperatures ({approx equal}300 {degree}C). The structures of the La, Pr, and Nd compounds appear related to that of Sr{sub 2}CuO{sub 3}, whereas those of the Sm, Eu, and Gd compounds are different. A new Nd{sub 2}CuO{sub 4}-type ({ital T}{prime}) La{sub 2}CuO{sub 4+{delta}} system was synthesized by oxidation of La{sub 2}CuO{sub 3.67} at 300--500 {degree}C; the oxygen contents are exceptionally high, ranging from 4.10 to 4.42. Annealing La{sub 2}CuO{sub 3.67} above 620 {degree}C in oxygen converts it to the original K{sub 2}NiF{sub 4}-type ({ital T}-phase) structure, but with excess oxygen (up to 4.06) and with smaller orthorhombicity compared to the La{sub 2}CuO{sub 4} starting material. Oxidation of the other {ital L}{sub 2}CuO{sub 3.5} phases ({ital L}=Pr,Nd,Sm,Eu,Gd) above 300 {degree}C leads to recovery of the original {ital T}{prime} structures, with oxygen contents ranging from 3.98 (Eu,Gd) to 4.03 (Nd). Magnetization measurements in a field of 50 G did not reveal superconductivity in any of the samples above 5 K.
- OSTI ID:
- 6227270
- Journal Information:
- Physical Review, B: Condensed Matter; (USA), Vol. 42:10; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COPPER OXIDES
SYNTHESIS
EUROPIUM OXIDES
GADOLINIUM OXIDES
LANTHANUM OXIDES
NEODYMIUM OXIDES
PRASEODYMIUM OXIDES
SAMARIUM OXIDES
ANNEALING
HYDROGEN
OXIDATION
PHASE TRANSFORMATIONS
REDUCTION
SUPERCONDUCTIVITY
CHALCOGENIDES
CHEMICAL REACTIONS
COPPER COMPOUNDS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
EUROPIUM COMPOUNDS
GADOLINIUM COMPOUNDS
HEAT TREATMENTS
LANTHANUM COMPOUNDS
NEODYMIUM COMPOUNDS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PRASEODYMIUM COMPOUNDS
RARE EARTH COMPOUNDS
SAMARIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies