The influence of carbon component structure of graphene containing shungite on its electrical conductivity.

Abstract

The investigation of the influence of carbon component structure of graphene containing shungite on its electrical conductivity is carried out. Five shungite samples from three different deposits with the same carbon content equal to 97% were selected as the object of research. It is established that the integral conductivity of specimens which is measured by four-contact method is changed in frames from 600 Sm/m to 2500 Sm/m. For the interpretation of so large scattering of data by equal concentration it was undertaken the investigation of carbon component structure on nano-level which was made by method of high-distinguish raster electron microscopy. By this method on the microscopic section of these specimens was obtained the cards of surface distribution of graphene slides and graphene packets. For the analysis of conductivity of specimens on the basis of these cards it was employed the method of independent channels. This method employs the presentation of specimen as a combination from parallel current-leading channels with following distribution of channel to cubic space blocks. The successive connection of blocks with accounting of slides orientation determines the total resistance of each channel and the parallel connections of all channels determines the specific conductivity of specimen as a whole. For the obtaining the quantity characteristics the whole card was distributed to some more small regions – fields. In this case the obtained results are averaged by the whole square of card. For the analysis of the field the method of square discretization was used. By this method the whole field id distributed to individual squares which dimension is near to the dimension of graphene packet. It was established that the character of structure in each square has two variants: first when the slides of graphene has clear determined spatial orientation ant the second when special orientation is absent and by orientation the squares are neutral. It is made the quantity analysis of neutral squares along the all specimens. It is shown that the normalized quantity of neutral squares is straight proportional to specific conductivity of specimen. The analysis of slides graphene orientation in squares with clear determined spatial orientation is carried out. For investigation of space structure of channel, the square was identified with lateral projection of block along two coordinates. The dependence of block resistance from the slide orientation is found. It is shown that the block resistance by the flowing of current across the graphene slides is more than order exceeds the resistance by the flowing of current along the slides of graphene. It is shown that the most role in formation of channel resistance play the blocks which graphene slides are oriented across the current flowing. By the adding of channels along the structure of volume unit it was founded the specific conductivity of specimen as a whole. It is established that the obtained meanings of conductivity for all specimens exceed the obtained by contact method on several times. As a reason of this exceeding it is established the absence of accounting the influence of enough small conductivity of intervals between slides and packets and also the absence of accounting of incomplete filling of squares by periodic structures. It is shown that the optimal in plane of correspondence to experiment is the introduce the normalization coefficient of conductivity of intervals which is equal to 0,2222. For the accounting of incomplete filling of squares by periodic structures it was carried out the binary discretization of most typical blocks with the resolution near 0,2 nm which is near the thickness of graphene slide. Along the obtained selection there was the averaged coefficients of filling of carbon which are equal from 0,10 to 0,15 parts for the whole volume of blocks. With the normalized conductivity of intervals and coefficients of filling of blocks it was found the integral conductivity for all specimens. It is shown that the obtained values are near the measured by contact method in the precision not more than 37%. In brief it is discussed the quality reason of apparent paradoxical increasing of integral conductivity by decreasing on structural character of carbon. It is established that the main reason of this increasing is the decreasing of contribution of graphene slides having large resistance which are oriented across the flowing of current.