Szymon Łoś

Photoactivity of g‐C3N4/S‐Doped Porous Carbon Composite: Synergistic Effect of Composite Formation

A composite of g-C3 N4 with visible-light photoactive S-doped carbon was synthesized. Synergistic effects in surface chemistry and electrical conductivity, and a decrease in the band gap (Eg , estimated from optical measurements) from 2.91 eV for g-C3 N4 to 2.79 eV for the composite were found. Both the carbon and the composite showed photosensitivity but only the composite revealed a visible-light-driven reduction activity.

Experimental techniques for the characterization of carbon nanoparticles - a brief overview

Summary The review of four experimental methods: X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance and four-point electrical conductivity measurements is presented to characterize carbon nanoparticles. Two types of carbon nanoparticle systems are discussed: one comprising the powder of individual carbon nanoparticles and the second as a structurally interconnected nanoparticle matrix in the form of a fiber. X-ray diffraction and Raman spectroscopy reveal the atomic structure of the carbon nanoparticles and allow for observation of the changes in the quasi-graphitic ordering induced by ultrasonic irradiation and with the so-called quasi-high pressure effect under adsorption conditions. Structural changes have strong influence on the electronic properties, especially the localization of charge carriers within the nanoparticles, which can be observed with the EPR technique. This in turn can be well-correlated with the four-point electrical conductivity measurements which directly show the character of the charge carrier transport within the examined structures.

Dielectric and EPR measurements of the deuterated glass D-RADA x=0.46

Abstract The results of the complex dielectric permittivity measurements and the spin-lattice relaxation times of the deuterated glass D-RADA x = 0.46, by the dielectric and EPR techniques are reported. The transition from paraelectric to antiferroelectric phase is detected at TN = 162 K. Below 90 K the dispersion of the complex dielectric permittivity was detected. The shape of the temperature dependence of the imaginary part of the dielectric permittivity was analyzed. This analysis shows the existence of two relaxation phases forming among the antiferroelectric domains, described by Arrhenius equation, and the glass state appears after the antiferroelectric ordering has been destroyed. The dielectric results are confirmed by the spin-lattice relaxation times data.

Intermediate phase between deuteron-glass and antiferroelectric order in the D-RADA system

Abstract This paper reports the results of a dielectric investigation of deuterated glass D-RADA, x = 0.39. The shape of the temperature dependence of the imaginary part of the permitivity e″ was analyzed. Analysis of the shape of the temperature dependence of e″(T, v) proved the existence of two phases of different mechanisms of relaxation, forming among the antiferroelectric domains. One of these mechanisms can be described by the Vogel-Fulcher equation with the parameters T0 = 25.7 K, Ec = 105.6 K (9.1 meV) and v0 = 1.16 × 108 Hz, and is typical for clusters with short-range order characteristic of proton (deuteron) glass. The other relaxational mechanism is the thermally activated Arrhenius dipolar reorientation with activation energy Ec = 1105 K (95.2 meV) and frequency vo = 1.44 × 1012 Hz. It is related to free dipoles which have been released from the melting long-range ordering but have not managed to form a cluster yet.

Dipolar glass-like dielectric response of nanocrystalline Sr0.95Nd0.05Fe12-xScxO19 hexaferrites

Recently reported magnetic quantum paraelectric properties in M-type hexaferrite single crystals have encouraged us to study the dielectric response of SrFe12O19 nanocrystallites down to the temperature of 10 K. As Sc-induced multiferroicity, promising for electromagnetic control, has been reported in bulk and films of hexaferrites, we also studied the size effect in dielectric response of Sr0.95Nd0.05Fe12-xScxO19 nanocrystallites with x = 0.36, 1.08, and 1.56. The nanopowders were obtained by citric method and the phase purity and the microstructure were controlled using X-ray diffraction and scanning electron microscopy. No clear evidence of quantum paraelectric behavior has been observed in temperature variation of dielectric permittivity of SrFe12O19 nanopowder. In the case of Nd-stabilized Sc-doped nanocrystallites, a low-temperature dielectric relaxation, similar to that in dipolar glasses, has been discovered. Activation energy of 62.5 meV was obtained for the lowest doping level and a modest increase in the energy was found at higher Sc concentrations. We relate the low-temperature relaxation in Sc-doped hexaferrite nanopowder to dielectric displacive polarization at the 4e Wyckoff sites modified by Sc-ions substituting the ferric ions in 4f2 and 12k positions.Recently reported magnetic quantum paraelectric properties in M-type hexaferrite single crystals have encouraged us to study the dielectric response of SrFe12O19 nanocrystallites down to the temperature of 10 K. As Sc-induced multiferroicity, promising for electromagnetic control, has been reported in bulk and films of hexaferrites, we also studied the size effect in dielectric response of Sr0.95Nd0.05Fe12-xScxO19 nanocrystallites with x = 0.36, 1.08, and 1.56. The nanopowders were obtained by citric method and the phase purity and the microstructure were controlled using X-ray diffraction and scanning electron microscopy. No clear evidence of quantum paraelectric behavior has been observed in temperature variation of dielectric permittivity of SrFe12O19 nanopowder. In the case of Nd-stabilized Sc-doped nanocrystallites, a low-temperature dielectric relaxation, similar to that in dipolar glasses, has been discovered. Activation energy of 62.5 meV was obtained for the lowest doping level and a modest incre...

EPR studies of NH2 + radicals created in the TGS: Fe3+ crystal after UV irradiation

Abstract Analysis of the radicals created in the TGS: Fe3+ crystal after UV-irradiation in the temperature 4.2 K using EPR technique are presented. Before UV-irradiation the low temperature (4.2 K) EPR spectra of TGS: Fe3+ due to Fe3+ ion is observed. After irradiation Fe3+ spectrum vanishes and new spectrum due to NH2 + radicals is observed. A model, based on the charge transfer from the ligands (NH2CH2COO)2 onto the central ion Fe3+, is presented.