Browsing by Author "Trubitsyn, Mykhailo P."

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    Composition Variations and UV Irradiation Effect on Charge Transfer in PbMoO4 Single Crystals
    (Oles Honchar Dnipro National University, 2022) Bochkova, Tatiana; Trubitsyn, Mykhailo P.; Volnianskii, M. D.; Volnyanskii, Dmytro M.
    ENG: The effect of nonstoichiometry of the composition, PbO polymorphism, and preliminary irradiation with ultraviolet light on electrical conductivity of alternating current (AC) was studied in PbMoO4 crystals. The crystals were grown by Czochralski method in a direction deviated by 30° from a-axis in (001) plain. The charge was prepared from MoO3 and PbO, lead oxide was used of α- or β- structural modifications. The reagents were taken both in a stoichiometric ratio and with an excess of 0.5 mol % of MoO3. It was shown that the magnitude of the dark and irradiation-induced AC conductivity was affected both by the type of polymorphic form of PbO and by the excess amount of MoO3. The influence of the PbMoO4 crystal structural disorder on charge transfer processes are discussed within the framework of the model of hopping conduction in disordered media.
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    Dielectric Properties of the Pb2MoO5 Crystals Irradiated with uv Light
    (Дніпровський національний університет імені Олеся Гончара, 2017) Volnyanskaya, I. P.; Trubitsyn, Mykhailo P.; Volnyanskii, Dmytro M.; Bondar, D. S.; Shvets, T. V.
    EN: The dielectric properties of the Pb2MoO5 crystals, exposed to UV light radiation (290 K), were studied. It was shown that UV irradiation led to appearance of permittivity maximum near 530 K (AC field frequency f=1 kHz). Heating up to 700 K resulted in thermal dissociation of the dipole complexes, induced by UV light irradiation and contributing to e peak. The magnitude of the e maximum increased with increasing time of UV light exposure and saturated for t>90 min. It is supposed that the observed anomaly of e is determined by dielectric response of (MoO3)- complexes. These centers arise when photoelectrons are trapped by molybdenum ions with oxygen vacancy VO in the nearest surroundings.
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    Phenomena Induced by UV Irradiation in PbMoO4 Single Crystal
    (Taylor & Francis, 2020) Bochkova, T. M.; Trubitsyn, Mykhailo P.; Volnyanskii, M. D.; Bondar, D. S.; Volnyanskii, Dmytro M.
    EN: Electrical properties and optical absorption of PbMoO4 single crystal were studied after UV irradiation. Anomalies of permittivity ε and conductivity σ were detected and attributed to the dipole centers induced by UV light. It was proposed that dipole centers were created by photoelectrons trapped by Mo within oxygen tetrahedra distorted by an oxygen vacancy VO. At high temperatures conductivity was nearly insensitive to UV irradiation. Additional optical absorption was observed in PbMoO4 single crystal after UV irradiation. It was argued that transfer of photoelectrons from lead to molybdenum groups was responsible for the photochromic effect found.
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    Photoinduced Effects in Single Crystals of PbO-MoO3 System
    (Institute of Physics PAS, Poland, 2022) Bochkova, Tatiana; Bondar, Dmytro; Trubitsyn, Mykhailo P.; Volnianskii, M. D.; Volnyanskii, Dmytro M.
    ENG: Purpose. Photoinduced changes in the optical absorption and dielectric properties of PbMoO4 and Pb2MoO5 crystals are considered. Differences in the manifestation of the photochromic effect in both crystals are associated with differences in their crystal structure. It is assumed that the photodielectric effect in the PbMoO4 and Pb2MoO5 crystals is due to the presence of the same anionic complexes. Methodology. Single crystals of PbMoO4 and Pb2MoO5 were grown in air from melt by the Czochralskii method. High-temperature treatment of the PbMoO4 crystals in air was carried out in a muffle furnace at 1200 K. The annealing time in the experiments varied from 2 to 90 h. Annealing of Pb2MoO5 crystals in vacuum was carried out at 1000 K during 1–2 h. The optical transmission spectra were measured at 295 K on the crystal doubly polished plates using a “Specord M-40” spectrophotometer. The photochromic coloration was observed after irradiation by light of Hg lamp during 2–5 h. Colored samples were returned to the initial state by annealing at 700–800 K in air for 2 h. Permittivity " was measured in the AC field by the four-wire method using a Keysight E4980AL LCR Meter at different frequencies (f = 1–10 kHz) in the temperature interval 290–700 K. Findings. One can assume that the photodielectric effect has the same nature and can be attributed for the common for both PbMoO4 and Pb2MoO5 crystals coordination complexes, i.e., molybdenum–oxygen tetrahedra. The dipole defects contributed to the photodielectric effect can be associated with Mo–O tetrahedra distorted by oxygen vacancy and photoelectrons capture. Hopping of VO through Mo–O tetrahedra vertices is accompanied by re-orientations of dipole moments of (MoO3)- complexes. Originality. Photoinduced changes in optical absorption and dielectric properties of PbMoO4 and Pb2MoO5 crystals are considered. The model of the mechanism of such changes of the power is offered. Practical value. The obtained conclusions will help to predict the influence of the composition of single crystals of acousto-optical materials of this series on their properties of practical value - optical absorption, optical stability..
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    Solid-Phase Synthesis and X-Ray Analysis of the Charge for Growing Acousto-Optic Pb2MoO5 Crystals
    (Дніпропетровський національний університет ім. Олеся Гончара, 2016) Volnyanskaya, I. P.; Trubitsyn, Mykhailo P.; Volnyanskii, Dmitriy M.; Kolessov, V. I.
    EN: Growing single crystals of double lead molybdate Pb2MoO5 is usually accompanied by the appearance of additional phases of PbO–MoO3 system. To improve quality of the grown crystals, it is necessary to provide single phase composition of the charge used. In the paper the regimes of the charge solid-phase synthesis are varied and the phase composition of the obtained charge is studied for the first time. The initial charge stoichiometry, number of stages of synthesis procedure, heating rate, temperature, and time of synthesis are varied in the experiment. X-ray phase analysis is performed for a number of the charge samples obtained under different technological conditions of solid-phase synthesis. It is shown that the appropriate choice of the synthesis regimes make it possible to reduce significantly the content of PbO–MoO3 impurity phases in the charge. The obtained results should make for increasing quality of Pb2MoO5 single crystals which are promising for use in acousto-optic devices.