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235 results on '"Samoggia, G."'

54. Defect structures and electronic properties in cubic stabilized zirconia

Author

Azzoni, C, Camagni, P, Samoggia, G, Paleari, A, Azzoni, CB, PALEARI, ALBERTO MARIA FELICE, Azzoni, C, Camagni, P, Samoggia, G, Paleari, A, Azzoni, CB, and PALEARI, ALBERTO MARIA FELICE

Abstract

EPR and optical absorption measurements have been performed to detect the defects activated by X-rays in single crystals of zinconium dioxide, stabilized in the cubic phase by the addition of Y2O3 in two different concentrations (12 and 24 mol%). Production yield and thermal stability confirm the attribution of the 375 nm optical absorption band to the defect responsible for the EPR T-signal. Deviations from a random distribution of the stoichiometric oxygen vacancies are evidenced. These results agree with the existence of ordering processes in the vacancy system, as predicted by recent structural models. © 1993.

Published
1993

57. Photoinduced charge effects in

Author

Banfi, G P, primary, Calvi, P, additional, Camagni, P, additional, Giulotto, E, additional, Rollandi, L, additional, Samoggia, G, additional, and Sangalli, P, additional

Published
1997
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69. Structural Phase Transition and Photo-Charge Carrier Transport in SrTiO 3.

Author

Galinetto, P., Rossella, F., Samoggia, G., Trepakov, V., Kotomin, E., Heifets, E., Markovin, P., and Jastrabik, L.

Subjects
FERROELECTRIC crystals, PHASE transitions, ELECTRONIC structure, SPECTRUM analysis, PHOTOCONDUCTIVITY
Abstract

The effect of the antiferrodistorsive phase transition observed at ∼⃒ 105 K on the photo-carriers transport and band structure of nominally pure SrTiO 3 single crystals was investigated. Simultaneously the ab-initio analysis based on the DFT-HF hybrid approach was performed in order to elucidate the atomic and electronic structure changes. It was found that the structural transition play a minor role in photo-charge transport. However, in highly resistive specimens at low UV-light intensities or under visible-light, 514 nm excitation, weak photoconductivity features are observed in the transition region. Besides, in this region the temperature maximum was found for the photoconductivity spectra. Experimental results are discussed and agree well with theoretical predictions. [ABSTRACT FROM AUTHOR]

Published
2006
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72. Ferroelectricity in K 0.992 Rb 0.008 Ta 0.96 Nb 0.04 O 3.

Author

Giulotto, E., Stasi, V., Galinetto, P., Rossella, F., Samoggia, G., Trepakov, V., Syrnikov, P., and Jastrabik, L.

Subjects
POTASSIUM, RUBIDIUM, TANTALATES, RAMAN effect, FERROELECTRICITY, FERROELECTRIC crystals
Abstract

We report on the first crystal growth and Raman scattering studies in K 0.992 Rb 0.008 Ta 0.96 Nb 0.04 O 3 (KRTN) and KTaO 3 :Rb (3% mol. in the melt), in which Rb + ions (ionic radius 1.47 Åt) substitute K + (1.33 Åt). The experiments were performed in the range 10–300 K and focused on the behavior of TO 1 and TO 4 modes. The results confirm indications by previous dielectric permittivity data about the ferroelectric nature of the phase transition in KRTN. It appears that a small amount of Rb changes the character of the phase transition induced by Nb from mainly displacive to mainly order-disorder, whereas no evidence of ferroelectricity is revealed in the KTaO 3 :Rb sample. [ABSTRACT FROM AUTHOR]

Published
2005
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79. Cluster size and long-range order in KNa TaO.

Author

Banfi, G. and Samoggia, G.

Abstract

We present second harmonic generation results which, for the first time, allow us to assess the correlation length of the order parameter exhibited by the mixed crystal K Na TaO. Our data, including linear birefringence results, evidence a transition to a polar state characterized, for a 15% Na doped sample, by clusters of size 0.12 to over 1 μm and a spontaneous polarization of 503 mC/m. Even if these findings can be consistent with a ferroelectric transition characterized by long-range order, precursor effects and the behaviour of hysteresis are more indicative of a glass-type transition. [ABSTRACT FROM AUTHOR]

Published
1988
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84. MAGNETIC-PROPERTIES OF SINTERED BACUO2

Author

AZZONI C.B., PALEARI A., PARRAVICINI G.B., SAMOGGIA G., SCAGLIOTTI M., PARMIGIANI, FULVIO, Azzoni, C. B., Paleari, A., Parravicini, G. B., Samoggia, G., Parmigiani, Fulvio, and Scagliotti, M.

Subjects
MAGNETIC-PROPERTIES, BACUO2
Published
1989

92. Optical field effect on the germanium surfaces

Author

Nucciotti, A. and Samoggia, G.

Abstract

In this paper we report some new measurements of field-effect modulated absorption for real surfaces of germanium. The spectra, taken for various values of the surface potential, show a broad band (α) at 0.39 eV and a narrow band (β) at 0.44 eV superimposed to a large background due to free-hole or free-electron absorption. The experimental data suggest the hypothesis that the «β»-band could arise from the change of the optical absorption of the OH vibrational line at 0.44 eV under the effect of the applied electric field. On the contrary the «α»-band seems due to electronic transitions from surface states to the conduction band. In questo lavoro si riportano nuove misure, sulle superfici reali del germanio, di assorbimento ottico modulato da effetto di campo. Gli spettri, presi per vari valori del potenziale di superficieus0, presentano una larga banda (α) a 0.39 eV e una stretta banda (β) a 0.44 eV sovrapposte ad un continuo dovuto ad assorbimento di cariche libere. I dati sperimentali suggeriscono l’ipotesi che la banda (β) sia dovuta alla variazione di assorbimento ottico sotto l’azione di un campo elettrico della riga vibrazionale del gruppo OH. Al contrario la banda (α) sembra dovuta a transizioni elettroniche da stati di superficie al fondo della banda di conduzione. В зтой статье мы сообшаем о некоторых новых иэмерениях влияния поля, модулируюшего поглошение для реальных поверхностей германия. Спектры для раэличных эначений поверхностного потенциала обнаруживают щирокую эону (α) при 0.39 зВ и уэкую эону (β) при 0.44 зВ, наложенные на больщой фон, обусловленный поглошением свободных дырок или свободных злектронов. Экспериментальные данные предполагают гипотеэу, что эона «β» может воэникать иэ иэменения оптического поглошения для вибрационной линии OH при 0.44 зВ, при действии приложенного злектрического поля. Напротив, эона «α», кажется, обусловлена злектронными переходами иэ поверхностных состояний в эону проводимости.

Published
1981
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98. Electric magnetic and thermodynamic anomalies observed in sintered copper oxide

Author

Paleari, A, Parmigiani, F, Parravicini, G, Ripamonti, N, Samoggia, G, Scagliotti, M, PALEARI, ALBERTO MARIA FELICE, Parravicini, GB, Scagliotti, M., Paleari, A, Parmigiani, F, Parravicini, G, Ripamonti, N, Samoggia, G, Scagliotti, M, PALEARI, ALBERTO MARIA FELICE, Parravicini, GB, and Scagliotti, M.

Abstract

This work presents structure, thermodynamic, magnetic and electric measurements performed on pure sintered CuO. Beside the known properties of CuO we observed anomalous thermodynamic, magnetic and electric behaviour in the temperature range between 230 K and 190 K strongly dependent on the story of the sample. A possible explanation of these effects could arise from Jahn-Teller dynamic distortions of the CuO6 bipyramidal structure that can be considerably influenced by the oxygen vacancies. Since these effects seem to be correlated with the superconducting properties observed in cuprate systems, further and more detailed experiments are in progress. © 1988.

Published
1988

99. Magnetic properties of sintered BaCuO2

Author

Azzoni, C, Paleari, A, Parravicini, G, Samoggia, G, Parmigiani, F, Scagliotti, M, Scagliotti, M., PALEARI, ALBERTO MARIA FELICE, Azzoni, C, Paleari, A, Parravicini, G, Samoggia, G, Parmigiani, F, Scagliotti, M, Scagliotti, M., and PALEARI, ALBERTO MARIA FELICE

Abstract

EPR susceptibility and XPS measurements were performed on sintered BaCuO2. A structured sharp EPR signal superimposed on a broad band was observed. It is shown that the structured line results from the superposition of two signals associated with divalent copper ions lying in two different distorted octahedral sites. These ions are probably placed on the outermost layer of the sintered grains. © 1989.

Published
1989

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