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Surface phonons of LaB6(100): deformation of boron octahedra at the surface
~542 Surtace Science 290 (1993) 427-435 North-Holland
Chemical changes induced by sputtering in TiO 2 and some selected titanates as observed by X-ray absorption spectroscopy L Sorlano 1, M. Abbate, J Vogel, J C Fuggle * Spectroscopy of Soltds and Surfaces, University of Nqmegen, Toernootceld, 6525 ED Nqmegen, Netherlands
A Fernfindez, A R Gonzfilez-Ehpe Instttuto de Clencla de Matertales de Sevdla, Dpto Qulmtca lnorgdmca, CSIC, Umverstdad de Sevdla, P O Box 1115, 41071 Sewlla, Spain
M Sacchl LURE, Umversitd Pans-Sud, B,~ttment 209 d, 91405 Orsay, France
and J M Sanz Depto Fistca Aphcada C-XII, UnwerswladAut6noma Madrid, Cantoblanco, 28049 Madrid, Spain Received 21 December 1992, accepted for pubhcatlon 24 February 1993 We studted the chemical changes induced by Ar+-bombardment m TtO 2 and some selected titanates by means of soft X-ray absorption spectroscopy The O ls and T~2p spectra provide umque mformatlon on hybndlzatlon, valency and crystal-field effects In TIO2, we found that some Tl tons are partly reduced but no metalhzatton is observed On the other hand, the effect of ion-bombardment m titanates depends on the counter-ions In Al2TiO5, the central Tl ions are strongly reduced whtle A1203 remams unaffected In NITRO3, by contrast, we found the opposite behavlour with strong reductson of the counter Nl ions This contrasting behaviour seems to be related to differences in the relative heat of formation of the sub-species In PbTiO3, both central- and counter-tons are affected by sputtering Finally, the electronic structure of BaTiO~ presents very httle changes upon ion-bombardment
Surface Sctence 290 (1993) 436-444 North-Holland
Surface phonons of LAB6(100)" deformation of boron octahedra at the surface Tadaakl Nagao *, Kazuo Kztamura, Yoslutaka hzuka, Chuhel Oshlma
1
Department of Apphed Physscs, Waseda Umverstty, 3-4-10kubo, Shmjuku-ku, Tokyo 169, Japan
and Shigeka Otani National lnstztute for Research m Inorgamc Matertals, 1-1 Nanukg Tsukuba, Ibarakt 305, Japan Received 29 December 1992, acceptable for pubhcatton 23 February 1993
The surface phonon dispersion of clean LAB6(100) surface has been measured by means of Mgh resolution electron energy loss spectroscopy Eight wbranonal modes, of which most are located m the energy gaps between the bulk phonon bands, have been detected The lattice dynanucal calculation of a slab-shaped crystal based on a force constant model has reproduced these expenmental dtspers~on curves, whmh indicates the large increase m the force constant of mteroctahedral boron-boron bond at the surface by 25%, and the large decrease m the force constants of mtraoctahcdral boron-boron bonds at the surface by 25-50% These changes together with the analysts of the bulk phonon structure of metal hexabondes strongly suggest that the boron octahedra at the surface are expanded by about 0 004 nm parallel to the surface
Chemical changes induced by sputtering in TiO 2 and some selected titanates as observed by X-ray absorption spectroscopy L Sorlano 1, M. Abbate, J Vogel, J C Fuggle * Spectroscopy of Soltds and Surfaces, University of Nqmegen, Toernootceld, 6525 ED Nqmegen, Netherlands
A Fernfindez, A R Gonzfilez-Ehpe Instttuto de Clencla de Matertales de Sevdla, Dpto Qulmtca lnorgdmca, CSIC, Umverstdad de Sevdla, P O Box 1115, 41071 Sewlla, Spain
M Sacchl LURE, Umversitd Pans-Sud, B,~ttment 209 d, 91405 Orsay, France
and J M Sanz Depto Fistca Aphcada C-XII, UnwerswladAut6noma Madrid, Cantoblanco, 28049 Madrid, Spain Received 21 December 1992, accepted for pubhcatlon 24 February 1993 We studted the chemical changes induced by Ar+-bombardment m TtO 2 and some selected titanates by means of soft X-ray absorption spectroscopy The O ls and T~2p spectra provide umque mformatlon on hybndlzatlon, valency and crystal-field effects In TIO2, we found that some Tl tons are partly reduced but no metalhzatton is observed On the other hand, the effect of ion-bombardment m titanates depends on the counter-ions In Al2TiO5, the central Tl ions are strongly reduced whtle A1203 remams unaffected In NITRO3, by contrast, we found the opposite behavlour with strong reductson of the counter Nl ions This contrasting behaviour seems to be related to differences in the relative heat of formation of the sub-species In PbTiO3, both central- and counter-tons are affected by sputtering Finally, the electronic structure of BaTiO~ presents very httle changes upon ion-bombardment
Surface Sctence 290 (1993) 436-444 North-Holland
Surface phonons of LAB6(100)" deformation of boron octahedra at the surface Tadaakl Nagao *, Kazuo Kztamura, Yoslutaka hzuka, Chuhel Oshlma
1
Department of Apphed Physscs, Waseda Umverstty, 3-4-10kubo, Shmjuku-ku, Tokyo 169, Japan
and Shigeka Otani National lnstztute for Research m Inorgamc Matertals, 1-1 Nanukg Tsukuba, Ibarakt 305, Japan Received 29 December 1992, acceptable for pubhcatton 23 February 1993
The surface phonon dispersion of clean LAB6(100) surface has been measured by means of Mgh resolution electron energy loss spectroscopy Eight wbranonal modes, of which most are located m the energy gaps between the bulk phonon bands, have been detected The lattice dynanucal calculation of a slab-shaped crystal based on a force constant model has reproduced these expenmental dtspers~on curves, whmh indicates the large increase m the force constant of mteroctahedral boron-boron bond at the surface by 25%, and the large decrease m the force constants of mtraoctahcdral boron-boron bonds at the surface by 25-50% These changes together with the analysts of the bulk phonon structure of metal hexabondes strongly suggest that the boron octahedra at the surface are expanded by about 0 004 nm parallel to the surface