1,721,003 research outputs found
Impurity effects and charge transport in ABO3 single crystal oxides: Photorefractivity-oriented and basic studies
No full textNon linear optical, dielectric, magnetic properties of ABO3 single crystal oxides let the implementation of acousto-optic, electro-optic, photonic, spintronic devices. In particular, significant role is played by the ferroelectric and photorefractive materials, where the photo-induced change in refractive indexes requires charge transport and impurities which support charge transfer, space charge formation and localization with accompanying electric field. Besides, ABO3 paraelectric perovskites regularly reveal newel effects connected with charge transport, e.g., photo-induced polar state recently reported for SrTiO3 and KTaO3. In this work we review our recent investigation, pointing out our studies of photo-transport in SrTiO3, Cu-doped KTaO3 and LiNbO3:Hf
Magnetic and Structural Studies in Co- and Mn-implanted SrTiO3 Single Crystals
No full textMicro Raman and static magnetization data on manganese or cobalt-implanted (at 3 or 5 at.%) strontium titanate (Mn,Co):SrTiO3 single crystals are presented. Micro Raman results reveal a cubic perovskite structure at 300 K with no evidence of any secondary phase. All samples show ferromagnetism both at 300 K and at 10 K. Moreover, micro Raman spectra at low temperature reveal the presence of polar ordering, which allow to consider the investigated materials as possible host matrices for multiferroic phenomena. Obtained results are discussed in connection to supplementary outcomes derived by content, optical absorption and electron paramagnetic resonance (EPR) measurements
Structural effects of Li and Nb codoping in a KTaO3 matrix: A Raman investigation
No full textRaman investigations on single crystals of K1-xLixTa1-yNbyO3 were performed to identify structural effects arising from the simultaneous presence of off-centre Li and Nb ions in the incipient ferroelectric KTaO3. Two soft-mode transitions were evidenced at 45K and 30K in a sample with x = 0.0014 and y = 0.024 after both zero-field and field cooling. These temperatures are close to the maximum and to the extrapolated Curie temperature for nonrelaxing permittivity reported in the same system. A sample with x = 0.0028 and y = 0.013 displayed a ferroelectric transition just below 30K only after field cooling, also being consistent with permittivity data
Raman study of Cu-doped K-1-xLixTa1-yNbyO3
No full textThe temperature evolution of TO1 Raman spectra was investigated in single crystals of K1.xLixTa1-yNbyO3:Cu with different Li and Nh amounts. Auxiliary observations of TO4 spectra were also performed. in a sample with x = 0.002 and y = 0.025 and containing 190 ppm of Cu, the results indicate a clear-cut transition to an ordered phase around 55 K, in good agreement with previous findings from dielectric measurements in the same crystal. However, no evidence was found of a role of Cu in this structural modification. Samples with x = 0.01 and y = 0.003 revealed features of an order-disorder phase transition around 45 K, irrespective of the presence of Cu
Ferroelectricity in K0.992Rb0.008Ta0.96Nb0.04O3
No full textThe paper reports on the first crystal growth and Raman scattering studies in K0.992Rb0.008Ta0.96Nb0.04O3 (KRTN) and KTaO3:Rb (3% mol. in the melt), in which Rb+ ions (ionic radius 1.47 angstrom) substitute K+(1.33 angstrom). The experiments were performed in the range 10-300 K and focused on the behavior of TO1 and TO4 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 KTaO3:Rb sample
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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