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Some studies of defects in calcium oxide - II intrinsic lattice defects
Vol.7, No.5 7.
ABSTRACTS OF PAPERS TO APPEAR IN
SOME STUDIES OF DEFECTS IN CALCIUM OXIDE —II INTRINSIC LATTICE DEFECTS B. Henderson and A.E. Tomlinson (Physics Department, Keele University, Keele, Staffordshire)
The optical absorption spectrum of electrolytically coloured calcium oxide shows the presence of both.F4- and F-centres. Low ternperature measurements of absorption and emission from the P’~-centresuggest that the electron-phonon coupling at the defect is strong enough to suppress the zero-phonon transition probability to undetectably small values, In electrolytically coloured crystals, although not in neutron irradiated crystals, the paramagnetic linewidth of the F+~centre43Ca is <15 mG, and the without isotopic hyperfine interaction from enrichment has been identified for the first time. Analysis of this hyperfine structure proves the de Boer model of the F~-centrein calcium oxide. There are further hyperfine interactions of the P+~centreelectron which have not been unambiguously identified. However, a group of lines has been assigned to an interaction with a nucleus having a spin I = 5/2: tentatively it is suggested that thisin 7O nuclides interaction is associated with ‘ the next-nearest-neighbour position.
Surprisingly, V,-centres are observed in these crystals after heat treatment alone. Enhancement V1-centre concentration u.v. irradiationofisthe more efficient than in the by isostructural magnesium oxide. Several spectra with identical symmetry but with different g-tensors from the V 1 -centre are apparently associated with holes trapped at cation vacancies near other defects. The magnetic resonance spectrum of the antimorph of the F-centre, corresponding to two trapped holes localised on opposite sides of the cation vacancy, has been identified. (Received 16 September 1968) (Revised 16 December 1968)
8.
J.
PHYS. CHEM. SOLIDS
iii
NONSTOICHIOMETRY IN RARE-EARTH FLUORIDES E. Catalano, R.G. Bedford, and V.G. Silveira (Lawrence Radiation Laboratory, University of California, Livermore, California) and H.H. Wickman (Bell Telephone Laboratories, Murray Hill, New Jersey)
We report the results of a systematic survey of the rare-earth fluoride systems at 1500°C. Stable fluorite phases with ideal composition LnF 2 were observed in the Sm, Eu, and Yb systems. A compound with this structure was also observed in the Tm system, but equilibrium was not established. The stable composition range of this phase in the Sm and Eu systems extends from LnF2~ to LnF225. A second phase of unresolved structure extends from LnF2~5to LnF 245 in the Sm and Eu systems. Additional unresolved phases are also present in the Yb system. SrnF3 (orthorhombic) is stoichiometric within experimental error. The lattice parameters of the fluorite phases decrease as fluorine is added. Bulk density measurements and X-ray densities indicate that the defect structure is due to Finterstitials. With the possible exception the Pr were and Nd systems, where slight color of changes observed in the LnF 3, no reactions occur between Ln and LnF3.at temperatures to 1600°C. Mbssbauer spectra of the Eu system indicate 2 or Eu~3state that thephases europium is in either The a Eu+ for all in the system. relaxation time for any charge transfer process is greater than l0’~ sec (the lifetime of the 151Eu nuclear excited state). Mössbauer spectra are consistent with the existence of the intermediate phases mentioned above. A few observations were made on mixed systems containing Sm + Pr and Sm + Nd fluorides. (Received 3 September 1968)
ABSTRACTS OF PAPERS TO APPEAR IN
SOME STUDIES OF DEFECTS IN CALCIUM OXIDE —II INTRINSIC LATTICE DEFECTS B. Henderson and A.E. Tomlinson (Physics Department, Keele University, Keele, Staffordshire)
The optical absorption spectrum of electrolytically coloured calcium oxide shows the presence of both.F4- and F-centres. Low ternperature measurements of absorption and emission from the P’~-centresuggest that the electron-phonon coupling at the defect is strong enough to suppress the zero-phonon transition probability to undetectably small values, In electrolytically coloured crystals, although not in neutron irradiated crystals, the paramagnetic linewidth of the F+~centre43Ca is <15 mG, and the without isotopic hyperfine interaction from enrichment has been identified for the first time. Analysis of this hyperfine structure proves the de Boer model of the F~-centrein calcium oxide. There are further hyperfine interactions of the P+~centreelectron which have not been unambiguously identified. However, a group of lines has been assigned to an interaction with a nucleus having a spin I = 5/2: tentatively it is suggested that thisin 7O nuclides interaction is associated with ‘ the next-nearest-neighbour position.
Surprisingly, V,-centres are observed in these crystals after heat treatment alone. Enhancement V1-centre concentration u.v. irradiationofisthe more efficient than in the by isostructural magnesium oxide. Several spectra with identical symmetry but with different g-tensors from the V 1 -centre are apparently associated with holes trapped at cation vacancies near other defects. The magnetic resonance spectrum of the antimorph of the F-centre, corresponding to two trapped holes localised on opposite sides of the cation vacancy, has been identified. (Received 16 September 1968) (Revised 16 December 1968)
8.
J.
PHYS. CHEM. SOLIDS
iii
NONSTOICHIOMETRY IN RARE-EARTH FLUORIDES E. Catalano, R.G. Bedford, and V.G. Silveira (Lawrence Radiation Laboratory, University of California, Livermore, California) and H.H. Wickman (Bell Telephone Laboratories, Murray Hill, New Jersey)
We report the results of a systematic survey of the rare-earth fluoride systems at 1500°C. Stable fluorite phases with ideal composition LnF 2 were observed in the Sm, Eu, and Yb systems. A compound with this structure was also observed in the Tm system, but equilibrium was not established. The stable composition range of this phase in the Sm and Eu systems extends from LnF2~ to LnF225. A second phase of unresolved structure extends from LnF2~5to LnF 245 in the Sm and Eu systems. Additional unresolved phases are also present in the Yb system. SrnF3 (orthorhombic) is stoichiometric within experimental error. The lattice parameters of the fluorite phases decrease as fluorine is added. Bulk density measurements and X-ray densities indicate that the defect structure is due to Finterstitials. With the possible exception the Pr were and Nd systems, where slight color of changes observed in the LnF 3, no reactions occur between Ln and LnF3.at temperatures to 1600°C. Mbssbauer spectra of the Eu system indicate 2 or Eu~3state that thephases europium is in either The a Eu+ for all in the system. relaxation time for any charge transfer process is greater than l0’~ sec (the lifetime of the 151Eu nuclear excited state). Mössbauer spectra are consistent with the existence of the intermediate phases mentioned above. A few observations were made on mixed systems containing Sm + Pr and Sm + Nd fluorides. (Received 3 September 1968)