V2O5 Single Crystals Research Articles

Pulsed laser deposition of VO2 thin films

High quality vanadium dioxide (VO2) thin films have been successfully deposited by pulsed laser deposition without postannealing on (0001) and (101̄0) sapphire substrates. X-ray diffraction reveals that the films are highly oriented with (010) planes parallel to the surface of the substrate. VO2 thin films on (0001) and (101̄0) substrates show semiconductor to metal transistions with electrical resistance changes as large as 4×104, 105, respectively. Thin films on (101̄0) substrate have a transition at as low as 55 °C with a hysteresis less than 1 °C. These transition properties are comparable with single crystal VO2.

Raman scattering and x-ray diffractometry studies of epitaxial TiO2 and VO2 thin films and multilayers on α-Al2O3(112̄0)

Epitaxial thin films of TiO2 and VO2 single layers and TiO2/VO2 multilayers were grown on (112̄0) sapphire (α-Al2O3) substrates using the metalorganic chemical vapor deposition technique and were characterized using Raman scattering and four-circle x-ray diffractometry. X-ray diffraction results indicate that the films are high quality single crystal material with well defined growth plane and small in-plane and out-of-plane mosaic. Single-layer films are shown to obey the Raman selection rules of TiO2 and VO2 single crystals. The close adherence to the Raman selection rules indicates the high degree of orientation of the films, both parallel and perpendicular to the growth plane. Selection rule spectra of two and three layer TiO2/VO2 multilayers are dominated by the VO2 layers with only minimal signature of the TiO2 layers. Due to the low band gap of semiconducting vanadium dioxide, we attribute the strong signature of the VO2 layers to resonant enhancement of the VO2 Raman component accompanied with absorption of the both the incident and scattered laser light from the TiO2 layers.

Two-photon absorption in V2O5 single crystals with Q-switched ruby laser pulses

New experimental results concerning the nonlinear absorption of V2O5 single crystals are reported. A Q-switched ruby laser have been used to measure the two-photon absorption coefficient at 694.3 nm. The results are analysed and interpreted with respect to the second-order attenuation of the light propagating through a plane-parallel medium.

SEM investigation on laser induced damage of V2O5 single crystals

physica status solidi (a)Volume 88, Issue 2 p. K119-K121 Short Note SEM investigation on laser induced damage of V2O5 single crystals L. Malicskó, L. Malicskó Research Laboratory for Crystal Physics, Hungarian Academy of Sciences, Budapest Search for more papers by this authorI. Hevesi, I. Hevesi Institute of Experimental Physics, Attila József University, Szeged Search for more papers by this authorL. Nánai, L. Nánai Institute of Experimental Physics, Attila József University, Szeged Search for more papers by this author L. Malicskó, L. Malicskó Research Laboratory for Crystal Physics, Hungarian Academy of Sciences, Budapest Search for more papers by this authorI. Hevesi, I. Hevesi Institute of Experimental Physics, Attila József University, Szeged Search for more papers by this authorL. Nánai, L. Nánai Institute of Experimental Physics, Attila József University, Szeged Search for more papers by this author First published: 16 April 1985 https://doi.org/10.1002/pssa.2210880246Citations: 2 POB 132, H-1502 Budapest 112, Hungary. H-6720 Szeged, Hungary. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume88, Issue216 April 1985Pages K119-K121 RelatedInformation

Sound speed determination in V2O5 single crystals using laser-generated acoustic waves

The application of laser-generated acoustic waves for the determination of sound velocities in solids is reported. As an example the longitudinal sound speed along the crystallographic b axis in vanadium oxide (V2O5) has been measured for the first time yielding a value of 3200 ms−1.

Electron Concentration in V2O5 Single Crystals as Determined by l/f Noise Measurements

Electron Concentration in V2O5 Single Crystals as Determined by l/f Noise Measurements

Damage of V2O5 Single Crystals by Powerful Pulsed CO2 Laser Irradiation

First experimental results are reported concerning V2O5 single crystals damage under the action of powerful pulsed CO2 laser radiation. On y rapporte les premiers resultats experimentaux concernant les dommages induits dans les monocristaux de V2O5 sous l'action d'un puissant laser pulse au CO2.

Anisotropy of x-ray emission spectra and electronic structure of V2O5 single crystals

The results of investigation of x-rayVK- andVL-emission spectra orientation dependence for V2O5-single crystals are reported. The applicability of different options of electronic structure cluster calculations for the interpretation of x-rayVK-emission bands anisotropy in V2O5-single crystal is discussed.

ESR of P2O5-doped V2O5 single crystals

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ESR of TeO2-doped V2O5 single crystals

ESR of TeO2-doped V2O5 single crystals

The mechanism of electrical threshold switching in VO2crystals

I-V characteristics of doped VO2 (0.8% Ti, 1.0% Al and 0.8% Cr) single crystals have been measured using a constant current source in the ambient temperature region 230 to 310K. The temperature of the crystal surface has also been measured. At switching the temperature of the crystal surface increases by only 3 to 6K above the ambient for different ambient temperatures. This suggests the formation of a current channel before switching. It is observed that the threshold voltage (Vth) increases but the current at switching (Ith) decreases with decreasing ambient temperature, giving a temperature-independent threshold power. The average critical power density at switching is 4.33*10-3 W mm-3 for different doped and undoped VO2 crystals. I-V measurements have also been made by placing electrodes on the crystal surface. It is observed that the threshold voltage increases with increasing electrode separation d but for d to 0 Vth gives a finite value. The ideal thermal models fail to give even qualitative agreement with the observed I-V and switching characteristics.

Electrical switching in single crystal VO 2

I–V characteristics of single crystal vanadium dioxide has been measured using a constant current source in the ambient temperature region 220–325°K. The temperature of the crystal surface has also been measured. It is observed that the switching voltage ( V th) increases but the current at switching ( I th) decreases with decreasing temperature, giving a temperature independent threshold power ( V th × I th). At switching, the temperature of the crystal surface increases only by 3–6°K above ambient for different ambient temperatures. These results can be qualitatively explained by assuming that a filament (channel) is formed before switching. The switching occurs when the temperature of this filament of finite width approaches the semiconductor-metal transition temperature. The initial width of the channel at switching decreases with decreasing temperature and at a given ambient temperature the channel width increases with increasing current in the post breakdown region.

Contact-Limited Conduction in V2O5 Single Crystals

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Metallic and semiconducting domains in switching VO2 single crystals

Abstract Visual effects observed in the process of switching of VO2 needles have been recorded on cine films and video tapes. During switching the samples split into semiconducting and metallic domains with simple geometrical shapes easily identified by their different colours. At constant currents some configurations are stable while others drift in the sense of the electric current. It is shown that this motion is driven by the Peltier effect at the two oppositely biased boundaries of each domain. The geometrical configurations of the domains, their and additional effects observed in the switching process of VO2 single crystals will be discussed in detail.

Metal-semiconductor domain configurations during switching of VO2single crystals

The geometry of stationary or mobile metallic and semiconducting domain configurations and their formation during the switching of a VO2 single crystal are discussed. It is shown that the motion of narrow semiconducting domains in the sense of the electric current is driven by the Peltier effect at the two oppositely biased interfaces. The Peltier heat may be partially or totally compensated for by thermal fluxes along temperature gradients in the supercooled metal and in the superheated semiconductor.

Proprietes electriques des phases de basse temperature M1, T et M2 dans VO2 dope au chrome et a l'aluminium

The electrical conductivity and thermopower have been measured on Cr and Al doped VO2 single crystals. The insulating M1, T and M2 phases have a similar behaviour with an activation energy Ea ≅0.40 eV. The conductivity halves abruptly at the T→M2 transition but no discontinuity is observed for the thermopower. The ansiotropy of the thermopower may be due to the anisotropic mobility of the holes in the lower quasi one dimensional Hubbard band.

Moving boundaries and travelling domains during switching of VO2single crystals

Coexisting metallic and semiconducting phases have been obtained by passing DC currents through VO2 single crystals. The mixed state was studied by optical microscopy. Narrow semiconducting strips that nucleate at the positive edge of a metallic domain and propagate towards its negative edge have been observed under constant currents.

Optical absorption of defects in V2O5 single crystals: V2O5 doped with Ti, Mo, and Cu

AbstractThe absorption spectra in the range from 0.3 to 2.1 eV of V2O5 single crystals doped with Ti, Mo, and Cu are presented. Besides of bands due to impurities, an enhanced absorption from oxygen vacancies is observed in Ti‐doped samples. Models of the various defect centres involved are discussed and it is shown that the absorption bands can be attributed to centres involving V4+ and an impurity. The model of Ballhausen and Gray for vanadyl complexes is used as a working model for the defects. Two weak bands are assigned to ligand field transitions of V4+. The more intense bands are assigned to charge transfer transitions into the orbitals of the neighbouring vanadium ions or the impurities.

Preparation and electric conductivity of V2O5 single crystals

AbstractPresent paper deals with the preparation of V2O5 single crystals, both pure and doped with Mg, Mn, and Fe respectively, by the method of zone melting. To verify the quality of crystals, measurements of electric conductivity were carried out in the direction perpendicular to cleavage plane (010). The results have shown that the prepared crystals are suitable for further investigation of physical properties.

Optical Absorption of Defects in V205 Single Crystals: As‐Grown and Reduced V2O5

AbstractAbsorption spectra are presented of V2O5 single crystals in the range 0.5 to 2.1 eV. From the behaviour of the optical absorption upon reduction, reoxidation, and annealing it follows that two different centres are active. The bands observed at 1.25 and 1.52 eV for a polarization parallel to the a‐axis (E‖a) and at 1.0 eV for E‖c increase after homogeneous reduction and are attributed to oxygen vacancies. The remaining structure in the range 0.6 to 1.1 eV is influenced by annealing and quenching and is probably due to a centre related with stacking faults. A possible centre is the V–V pair proposed by Perlstein.