Transport properties near the metal-insulator transition in heat-treated activatedrotect carbon fibers

Raman scattering, x-ray diffraction, and BET measurements are used to study the effect of heat treatment on the microstructure of activated carbon fibers (ACFs) and to correlate the structural changes with the metal-insulator transition observed in the electronic transport properties of heat-treated ACFs. A sequence of events is identified, starting with desorption, followed by micropore collapse plus the stacking of basic structural units in the c-direction, and ending up with in-plane crystallization. The graphitization process closely resembles that depicted by Oberlin's model, except that the final material at high-temperature heat treatment remains turbostratic. Because the metal-insulator transition was observed to occur at heat-treatment temperature THT ≃ 1200 °C, which is well below the THT value (2000 °C) for in-plane crystallization, we conclude that this electronic transition is not due to in-plane ordering but rather to the collapse of the micropore structure in the ACFs. Raman scattering also provides strong evidence for the presence of local two-dimensional graphene structures, which is the basis for the transport phenomena observed in heat-treated ACFs.

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Transport properties of two-dimensional hole gas in a Ge1−x Si x /Ge/Ge1−x Si x quantum well in the vicinity of metal-insulator transition

Semiconductors ◽

10.1134/s1063782607110085 ◽

2007 ◽

Vol 41 (11) ◽

pp. 1315-1322 ◽

Cited By ~ 1

Author(s):

Yu. G. Arapov ◽

V. N. Neverov ◽

G. I. Harus ◽

N. G. Shelushinina ◽

M. V. Yakunin ◽

...

Keyword(s):

Quantum Well ◽

Transport Properties ◽

Insulator Transition ◽

Two Dimensional ◽

Metal Insulator Transition ◽

Metal Insulator

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Magnetic, Electronic - and Magneto - Transport Properties of Nanocrystalline Nd0.6Sr0.4MnO3 Manganites

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.67.131 ◽

2009 ◽

Vol 67 ◽

pp. 131-136 ◽

Cited By ~ 3

Author(s):

Kundu Sourav ◽

Kumar Nath Tapan

Keyword(s):

Particle Size ◽

Grain Size ◽

Transition Temperature ◽

Curie Temperature ◽

Transport Properties ◽

Significant Variation ◽

Insulator Transition ◽

Metal Insulator Transition ◽

Metal Insulator ◽

Low Field

We have reported in this paper, the effect of grain size in Nd0.6Sr0.4MnO3 .We have investigated the effect of grain size on metal-insulator transition and Curie temperature. We have also reported here the variation of low field magnetoresistance with temperature and grain size. We have observed that the Curie temperature increases monotonically with particle size. The metal insulator transition temperature initially increases with particle size and then gets fixed to a certain value. In these Nd0.6Sr0.4MnO3 nanometric systems, any significant variation of magnetoresistance with particle size is not observed.

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TRANSPORT PROPERTIES OF Ag-DOPED La0.7Ca0.3MnO3 THIN FILMS ON SILICON SUBSTRATE

International Journal of Modern Physics B ◽

10.1142/s0217979210056141 ◽

2010 ◽

Vol 24 (27) ◽

pp. 5451-5456 ◽

Cited By ~ 1

Author(s):

H. C. JIANG ◽

W. L. ZHANG ◽

X. F. CAO ◽

W. X. ZHANG ◽

B. PENG

Keyword(s):

Thin Films ◽

Transition Temperature ◽

Transport Properties ◽

Silicon Substrate ◽

Annealing Temperature ◽

Rf Magnetron Sputtering ◽

Insulator Transition ◽

Metal Insulator Transition ◽

Metal Insulator ◽

Higher Temperature

Ag -doped La 0.7 Ca 0.3 MnO 3 (LCMO) films were prepared on silicon substrate by RF magnetron sputtering. The dependences of transport properties on annealing temperature were explored. It is shown that the resistivity of the samples decreases and the metal–insulator transition temperature shifts to higher temperature with the increase in annealing temperature. Two metal–insulator transition temperatures are presented in the R – T plots of Ag -doped LCMO films, which can be explained by the Ag 1+ substitution of La 3+ to form La 1-x Ag x MnO 3 compound. Compared with LCMO thin films, Ag -doping can observably improve the TM-I and decrease the resistivity of the samples.

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The Influence of Local Magnetization on Transport in Cd0.91Mn0.09Te:In

MRS Proceedings ◽

10.1557/proc-290-335 ◽

1992 ◽

Vol 290 ◽

Cited By ~ 1

Author(s):

S. Von Molnar ◽

T. Penney ◽

I. Terry ◽

P. Becla

Keyword(s):

Transport Properties ◽

Carrier Concentration ◽

Magnetic Semiconductors ◽

Localization Length ◽

Insulator Transition ◽

Local Magnetization ◽

Metal Insulator Transition ◽

Metal Insulator ◽

Magnetic Polarons ◽

Transport Effect

AbstractWe describe the influence of local magnetization on electron localization and transport properties on the insulating side of the metal insulator transition in the dilute magnetic persistent photoconductor Cd0.091 Mn0.09Te:ln. Measurements of both the temperature dependence of the transport properties, and also the dielectric constant, are reported for just one sample in which the carrier concentration n was varied by photodoping. From these results we are able to extract the carrier concentration dependence of the localization length and the permitivity of the electrons. We also report onl a new transport effect which occurs at ultra low temperatures and/or carrier concentrations very close to the metal insulator transition. We find that this mechanism is totally magnetic in origin and are able to explain it in terms of the well devewloped ideas of magnetic polarons in magnetic semiconductors.

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Fabrication and Transport Properties of Manganite-Polyacrylamide-Based Composites

Journal of Nanomaterials ◽

10.1155/2009/429430 ◽

2009 ◽

Vol 2009 ◽

pp. 1-5 ◽

Cited By ~ 1

Author(s):

Viorel Sandu ◽

Stelian Popa ◽

Ion Ivan ◽

Carmen Plapcianu ◽

Elena Sandu ◽

...

Keyword(s):

Transport Properties ◽

Insulator Transition ◽

Electric Transport ◽

Metal Insulator Transition ◽

Metal Insulator ◽

Poly Acrylamide

We present the fabrication and transport properties of a series of composites made ofLa2/3Sr1/3MnO3and acrylamide-based copolymers. The most important result is the very narrow transition, of only 27 K, displayed by the peak that appears around the metal-insulator transition of the composites made with poly(acrylamide-vinylacetate). Although the amount of polymer is rather low, different copolymers change drastically the electric transport characteristics.

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