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Transverse magnetoresistance peculiarities of thermoelectric Lu-doped Bi_2Te_3 compound due to strong electrical disorder

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Journal of Rare Earths 2019年第3期37卷 292-298页

作者： Oleg Ivanov Maxim Yaprintsev Elena Danshina belgorod state university belgorod state technological university named after v.g.Shukhov

The n-type thermoelectric Bi_(1.9)Lu_(0.1)Te_3 was prepared by microwave-solvothermal method and spark plasma sintering. The magnetic field and temperature dependences of transverse magneto resistance measured within temperature 2-200 K interval allow finding the peculiarities characteristic for strongly disordered and inhomogeneous semiconductors. The first peculiarity is due to appearance of linear-inmagnetic field contribution to the total magneto resistance reflected in a crossover from quadratic magnetoresistance at low magnetic fields to linear magneto resistance at high magnetic fields. The linear magnetoresistance can result from the Hall resistance picked up from macroscopically distorted current paths due to local variations in stoichiometry of the compound studied. The second peculiarity is that both linear magnetoresistance magnitude and crossover field are functions of carrier mobility which is in agreement with the Parish and Littlewood model developed for disordered and inhomogeneous semiconductors. An increase in the mobility due to a decrease in temperature is accompanied by an increase in the magnetoresistance magnitude and a decrease in the crossover field. Finally, the third peculiarity is related to the remarkable deviation of the total magnetoresistance measured at various temperatures from the Kohler's rule. Presence of strong inhomogeneity and disorder in the Bi_(1.9)Lu_(0.1)Te_3 structure concluded from the magnetoresistance peculiarities can be responsible for the remarkable reduction in the total thermal conductivity of this compound.

关键词： Bismuth telluride Linear positive magnetoresistance Semiconductors Thermoelectric material Carrier mobility Kohler’s rule

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Preparation of crystalline Mg(OH)2 nanopowder from serpentinite mineral

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International Journal of Mining Science and Technology 2018年第3期28卷 499-503页

作者： v. Sirota v. Selemenev M. Kovaleva I. Pavlenko K. Mamunin v. Dokalov M. Yapryntsev belgorod state National Research university Belgorod 308015 Russia voronezh state university Voronezh 394006 Russia belgorod state technological university named after v.g. shoukhov Russia

In this paper we describe a route to produce crystalline Mg（OH）2 nanopowders from serpentinite ore distributed in the Halilovskiy array （Russia, Orenburg region）. An efficient extraction route consisting of treatment on serpentinite in 40% HNO3 at 80 ℃followed by NH4OH titration for Mg（OH）2 precipitation was demonstrated. In this study, crystalline Mg（OH）2 nanopowders have been synthesized by solvothermal reaction method using （Mg（NO3）2·6H2O） which were obtained from serpentinite, NH4OH as a precipitator, and hydroxyethylated nonylphenol as surface-active substance. Microstructure and phase composition of samples were investigated employing scanning electron microscopy （SEM） and transmission electron microscopy （TEM）, X-ray phase analysis （XRD）, and inductively coupled plasma optical emission spectroscopy （ICP-OES）. XRD reveals that Mg（OH）2 nanopowder with high purity has the brucite structure. It was found that crystalline Mg（OH）2 nanopowders exclusively consist of lamellar-like structures and the sizes of Mg（OH）2 are 30-265 nm length or width.

关键词： Serpentinite Nitric acid leaching Magnesium hydroxide Solvothermal reaction method Crystalline Mg(OH)2 nanopowder

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The effect of SiO2 nanoparticles derived from hydrothermal solutions on the performance of portland cement based materials

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Frontiers of Earth Science 2017年第4期11卷 436-445页

作者： Ismaei FLORES-vIvIAN Rani g.K PRADOTO Mohamadreza MOINI Marina KOZHUKHOvA vadim POTAPOv Konstantin SOBOLEv Department of Civil Engineering and Mechanics Advanced and Nano Cement-Based Materials Laboratory University ofWisconsin-Milwaukee Milwaukee 53211 USA Universidad Aut6noma de Nuevo Le6n Av. Universidad s/n Cd. Universitaria San Nicoldts de los Garza 66455 Nuevo Le6nMExico The belgorod state technological university named after v.g. shoukhov Belgorod Russia geotechnological Research Center Far East Branch of Russian Academy of Science Petropavlovsk-Kamchatsky 683002 Russia

The nanoparticles of SiO2 were used in cement systems to modify the rheological behavior, to enhance the reactivity of supplementary cementitious materials, and also to improve the strength and durability. In this research, low-cost nano-SiO2 particles from natural hydrothermal solutions obtained by membrane ultrafiltration and, optionally, by cryochemical vacuum sublimation drying, were evaluated in portland cement based systems. The SiO2-rich solutions were obtained from the wells of Mutnovsky geothermal power station （Far East of Russia）. The constant nano-SiO2 dosage of 0.25% （as a solid material by weight of cementitious materials） was used to compare the cement systems with different nanoparticles against a reference mortar and a commercially available nano-SiO2. Nanoparticles were characterized by X-Ray Diffraction （XRD）, BET Surface Area, Scanning Electron Microscope （SEM） and Fourier Transform Infrared （FTIR） spectroscopy techniques. It was demonstrated that the addition of polycarboxylate ether superplasticizer and the dispersion treatment using an ultrasound processor can be used to facilitate the distribution ofnano-SiOz particles in the mixing water. The effect ofnano-SiO2 particles in portland cement mortars was investigated by evaluating the flow, heat of hydration and compressive strength development. It was demonstrated that the use ofnano- SiO2 particles can reduce the segregation and improve strength properties.

关键词： ultrafiltration cryochemical vacuum sublimation drying nanoparticles portland cement heat of hydration,surface area compressive slxength

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