Unit:
Κατεύθυνση Φυσική των Υλικών (ΒΑΣΙΚΗ ΦΥΣΙΚΗ)Library of the School of Science
Supervisors info:
Ε. Συσκάκης Επίκ.Καθηγητής (Επιβλέπων), Μ.Καλαμιώτου Καθηγήτρια , Δ.Σταμόπουλος Αναπλ. Καθηγητής
Original Title:
Παρασκευή λεπτών στρωμάτων/υμενίων οξειδίων του Βαναδίου και ηλεκτρικός χαρακτηρισμός τους στην περιοχή 80_x0014_?Τ_x0014_?500 Κ
Translated title:
Preparation of thin layers/films of vanadium oxides and their electrical characterization in the range 80?T?500K
Summary:
In the present work, the electrical properties of thin PVD films, as well as of
sintered and dense layers of V2O5 and VO2 deposited on Y-ZrO2 and Si substrates
were investigated by electrical resistivity R(T) measurements and
current-voltage (I-V) characteristics in the range 80-550 K. The VO2 layers
were obtained by vacuum (10-2mbar) reduction of V2O5 layers at T= 480-600 oC
for t=1-12 hours. Τhe phase constitution and microstructure of the specimen
were examined by X-ray Diffraction (XRD) and scanning electron microscopy
(SEM), respectively.
According to the results the electrical conductivity of the V2O5 specimen can
be attributed to thermally activated hopping of small polarons between V4+ and
V5+. Both the conductivity as well as the corresponding activation energy
depend strongly on the microstructure of the specimen. In the reduced specimen
the XRD identification analysis shows, apart from the VO2 layer, coexistence of
V6O13 and/or V2O5. Nevertheless, an abrupt drop has been observed in the R(T)
measurements at TMIT=330 K which is attributed to the metal insulator
transition (MIT) in the VO2 layer. The thermally activated MIT takes place
within 1-2 K and is accompanied by small (2-4 K) hysteresis, while the
resistance drops by up to 3 orders of magnitude. Both the R(T) data as well as
the I-V characteristics provide conclusive evidence that the MIT can also be
triggered by an external dc electric field.
Keywords:
Vanadium oxides, Electrical conductivity, Small polaron, Metal-insulator transition (MIT), Vacuum reduction
