Studies of pure and Fe doped YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]]

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7303098

Siddique, R K

YBa[sub 2](Cu[sub 1[minus]x]Fe[sub x])O[sub 7[minus][delta]] (YBCO) compounds for x = 0.0, 0.01, 0.02, 0.05, 0.15, and 0.25 were studied. Samples include fully oxygenated virgin, and oxygen deficient samples, and the oxygen deficient samples after reoxygenation. X-ray diffraction, oxygen content, and magnetization measurements were used for obtaining information respectively on crystal structure, oxygen stoichiometry, and superconducting (SC) critical temperature (T[sub c]). By isothermal vacuum annealing (VA) pure (x=0) YBCO superconducting samples in the temperature range 300-800C, some important results such as: (1) the steplike increase of c axis length, and (2) the familiar plateaus in T[sub c] with oxygen stoichiometry were reproduced. For x = 0.02-0.05, the symmetry of crystal changed from orthorhombic to tetragonal, and for x = 0.25, sample became non SC. The authors find evidence that the Fe-O bonds in YBCO are stronger than the Cu-O bonds. Moessbauer studies of Fe doped virgin samples; by VA these virgin samples at 800C; and reoxygenating these oxygen desorbed samples at 410C were used for identifying Fe sites, and for determining oxygen coordination of Fe. Only three quadrupole doublets each corresponding to an Fe site were sufficient to fit room temperature (RT) Moessbauer spectra of virgin samples for x [le] 0.15, while for x = 0.25, two additional magnetic sextets had to be added. The subspectra are explained in terms of square planar, pseudotetrahedral, and octahedral oxygen environment around Fe atoms in the crystal. Due to vacuum annealing samples at T[sub a] [ge] 400C, new Fe sites appeared in all RT spectra, and depending on the value of x, and the annealing temperature, T[sub a], one or two magnetic sites evolved. From the Moessbauer spectra of virgin (x = 0.25 only), and oxygen deficient samples as a function of temperature the authors determined the magnetic ordering temperature, T[sub N].

• Research Organization: Cincinnati Univ., OH (United States)
• OSTI ID: 7303098
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360207* -- Ceramics
Cermets
& Refractories-- Superconducting Properties-- (1992-)
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
CRYSTAL DOPING
CRYSTAL STRUCTURE
CUPRATES
HIGH-TC SUPERCONDUCTORS
INTERMETALLIC COMPOUNDS
IRON ADDITIONS
IRON ALLOYS
MOESSBAUER EFFECT
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
STOICHIOMETRY
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE
YTTRIUM COMPOUNDS
YTTRIUM OXIDES