Regensburg 2000 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Supraleitende Anwendungen (1-4) Massive HTSL, Bandleiter, Filme (5-26), Transport in HTSL (27-30), Elektronenstruktur in Supraleitern (31-43), Borkarbide (44-50), Quantenphasen- und Metall-Isolator-Überg
änge (51-69)

TT 22.56: Poster

Donnerstag, 30. März 2000, 14:00–17:30, A

Electrical Conductivity and Current Transport Mechanism in Ion Implanted TiO₂-Single Crystals — •R. Fromknecht¹, O. Meyer², I. Khubeis², S. Massing¹, R.C. da Silva³, and E. Alves³ — ¹Forschungszentrum Karlsruhe, IFP, 76021 Karlsruhe — ²Al-Balqa Appl. Univ., Al-Salt, Jordan — ³Dep. Fisica, ITN-E.N.10, 2685 Sacavem

TiO₂ single crystals, implanted at low and elevated temperatures, with 15 different ions using fluences from 10¹⁴/cm² to 10¹⁷/cm² at E_i = 260 keV. Lattice site location, ion range and damage distribution were measured by Rutherford Backscattering Channeling. The electrical conductivity of those samples, measured between 5 and 300 K, with the ion dose, the implantation temperature and the annealing conditions (air, vacuum) as parameter, increased by about 12 orders of magnitude with increasing ion dose. Samples implanted at 300 K and below, their resistivity was thermally activated over the whole temperature region, indicating carrier hopping. The T⁻¹ dependence observed at low doses implies localized defect states. With increasing defect density, states with different energy levels, localized in the gap, are formed and the electron transport is due to variable range hopping (VRH), as indicated by the T^−1/4 dependence at high doses. The T^−1/2 dependence observed at medium doses, attributed to VRH with a pseudogap near the Fermi energy, due to long range Coulomb interaction between carriers. Samples implanted at high temperatures or annealed in vacuum, showed metallic behaviour between about 30 K and 100 K. Concluded from annealing experiments in air, oxygen vacancies seem to be the main defect causing this behaviour.