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LEED study of NaxWO3 tungsten bronze: structural relaxation of a perovskite surface
A392 Surface Science 287/288 (1993) 400-402 North-Holland
RHEED study of the (0001)LiNbO 3 surface annealed at high temperature E.V. Rakova Institute of Crystallography, Russian Academy of Science, Leninsky Prospekt 59, 117333 Moscow, Russian Federation Received 21 August 1992; accepted for publication 26 November 1992 The surface structure of (0001)LiNbO 3 plates annealed in air at a temperature of 950-1150°C is studied by RHEED. After annealing the reflections of fractional indices are observed in diffraction patterns; they vanish after a short-time etching of the surface with acids. The origin of superstructure reflections is discussed.
Surface Science 287/288 (1993) 403-408 North-Holland
LEED study of NaxWO 3 tungsten bronze: structural relaxation of a perovskite surface S.D. Peacor and T. Hibma Department of Chemical Physics of the University of Groningen, Nijenborgh 4, 9747AG Groningen, Netherlands Received 31 August 1992; accepted for publication 7 October 1992 We have performed a low energy electron diffraction study of the sodium tungsten bronze, NaxWO3, x = 0.8, surface. Temperature dependent changes of both polished and cleaved surfaces indicate structural phase transitions of the surface structure, and reflect the general trend in structural phase transitions of the bulk. Surface phase transitions take place, however, at higher temperatures, indicating a relaxation of the surface of this perovskite structure. In addition, sodium ordering in non-equivalent sites modifies the LEED patterns. We show that our description also applies to the data previously reported by other groups covering a larger range of sodium concentration x. Our measurements indicate that the surface structure is sensitive to sample heating, displaying an irreversible change near 600°C.
Surface Science 287/288 (1993) 409-413 North-Holland
Charge-density wave modulation in surface layers of TaS 2 and NbS2 M. Rem~kar, A. Prodan and V. Marinkovid 3. Stefan Institute and Department of Metallurgy, University of Ljubljana, Ljubljana, Slovenia Received 1 September 1992; accepted for publication 19 November 1992 NbS 2, TaS 2 and NbSe 2 layered crystals were studied by means of scanning tunneling microscopy and transmission electron diffraction. NbSe 2 showed a well ordered atomic surface only and TaS2 a strong nearly commensurate charge-density wave modulation, both in agreement with earlier observations. Contrary, NbS~ surfaces displayed a corrugation with the periodicity of NbS2 lattice but with irregular amplitude fluctuations. Two possible structural models for this effect are discussed.
RHEED study of the (0001)LiNbO 3 surface annealed at high temperature E.V. Rakova Institute of Crystallography, Russian Academy of Science, Leninsky Prospekt 59, 117333 Moscow, Russian Federation Received 21 August 1992; accepted for publication 26 November 1992 The surface structure of (0001)LiNbO 3 plates annealed in air at a temperature of 950-1150°C is studied by RHEED. After annealing the reflections of fractional indices are observed in diffraction patterns; they vanish after a short-time etching of the surface with acids. The origin of superstructure reflections is discussed.
Surface Science 287/288 (1993) 403-408 North-Holland
LEED study of NaxWO 3 tungsten bronze: structural relaxation of a perovskite surface S.D. Peacor and T. Hibma Department of Chemical Physics of the University of Groningen, Nijenborgh 4, 9747AG Groningen, Netherlands Received 31 August 1992; accepted for publication 7 October 1992 We have performed a low energy electron diffraction study of the sodium tungsten bronze, NaxWO3, x = 0.8, surface. Temperature dependent changes of both polished and cleaved surfaces indicate structural phase transitions of the surface structure, and reflect the general trend in structural phase transitions of the bulk. Surface phase transitions take place, however, at higher temperatures, indicating a relaxation of the surface of this perovskite structure. In addition, sodium ordering in non-equivalent sites modifies the LEED patterns. We show that our description also applies to the data previously reported by other groups covering a larger range of sodium concentration x. Our measurements indicate that the surface structure is sensitive to sample heating, displaying an irreversible change near 600°C.
Surface Science 287/288 (1993) 409-413 North-Holland
Charge-density wave modulation in surface layers of TaS 2 and NbS2 M. Rem~kar, A. Prodan and V. Marinkovid 3. Stefan Institute and Department of Metallurgy, University of Ljubljana, Ljubljana, Slovenia Received 1 September 1992; accepted for publication 19 November 1992 NbS 2, TaS 2 and NbSe 2 layered crystals were studied by means of scanning tunneling microscopy and transmission electron diffraction. NbSe 2 showed a well ordered atomic surface only and TaS2 a strong nearly commensurate charge-density wave modulation, both in agreement with earlier observations. Contrary, NbS~ surfaces displayed a corrugation with the periodicity of NbS2 lattice but with irregular amplitude fluctuations. Two possible structural models for this effect are discussed.