| Small amounts of doping materials can often make a dramatic change in the nature, and sometimes exhibit unusual properties, especially in the doped semiconductor. The resistivity of silver selenide and silver telluride(referred to as silver chalcogenide) in the case of an external magnetic field change, which is due to the movement of electrons by the Lorentz force effect, known as the normal magnetoresistance effect, and most semiconductor materials are of such a nature. However, the magnetoresistance usually is small. Self-doped nonstoichiometric silver chalcogenides have shown unusually large, positive and linear magnetoresistance effect (LMR), which exhibits a linear dependence on magnetic field from 1mT to 55T in the range of temperature from 4K to 300K. This peculiar phenomenon has aroused wide attention.Homogeneous and non- homogeneous silver selenide (Ag~2 +δSe (δ≥0)) crystal are prepared by two-step method for the first time. First Silver selenide powder prepared by chemical deposition method and the bulk prepared by solid state method. Combined with X-ray diffraction analysis, scanning and transmission electron microscopy, the phase and the topography were characterized. The results showed thatα-phase Ag~2Se manometer particles with a high purity and orthorhombic structure were obtained; During the process silver selenide powder prepared by chemical deposition, the reaction time is a very important parameters. the results showed thatα-phase silver selenide with a high purity and orthorhombic structure are obtained ,only when the time is 10h. The silver selenide bulk prepared by the solid state method has low sintering temperature, has less volatile materials and is very dense. The highest sintering temperature and the holding time of the highest temperature are also important process parameters. According to the study , completed- crystallized Ag 2 +δSe crystals can be obtained from the sintering temperature between 450℃to 500℃. Moreover, the dense of crystals were improved when sintered in flowing argon of crystals and cooling rate have a great impact on the microstructure of the sample.Firstly, selenium proportion in chemical equation was changed and silver selenide nanoparticles with different silver excess ( Ag~2+δSe(δ≥0))were prepared by chemical deposition method, and then were sintered into crystals by solid state method. the result of XRD and FSEM show that the sample is the standard of silver selenide when the natural cooling to the room temperature (30℃/h). while the trends of the lingitudinal growth of the samples happened if cooling quickly (200℃/h). Silver excess has an impact on the growth of silver selenide. With the excess of silver increased, the grain of silver selenide size decreases but not limitless. there were more excess silver which exists as atoms or clusters and arranged chainlike in the grain boundary of silver selenide . we do some research on the physical properties of silver selenide with silver excess ,especially the linear magnetoresistance in pulsed magnetic. the result showed that the resistance-temperature characteristeics of non-stoichiometric silver selenide is consistent with that of semiconductor; t lower temperature, the thermal scattering is dominant and the resistivity increases with the increasing of temperature; when the temperature increases to a value, there are a large number of carriers because of the dominance of the intrinsic excitation, then the resistivity began to decrease. The MR effect becomes larger in the pulse magnetic field and the positive effect is almost linear in its field dependence. However, Field dependence for our samples was nonlinear at a field less than 3T or 4T. The field is different with the difference of the excess Ag of silver selenide. We also find the positive MR which decreases with increasing temperature. |
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