ELECTRICAL CONDUCTIVITY OF SEVERAL SAMPLES OF OLIVINITES, PERIDOTITES, AND DUNITES, AS A FUNCTION OF PRESSURE AND TEMPERATURE

Geophysics ◽  
1973 ◽  
Vol 38 (1) ◽  
pp. 14-24 ◽  
Author(s):  
Z. Dvořák
Keyword(s):  
Electrical Conductivity ◽  
Low Temperature ◽  
Temperature Interval ◽  
Geomagnetic Variation ◽  
Conductivity Data ◽  
Exponential Term ◽  
Temperature Range ◽  
The Earth ◽  
Straight Line ◽  
Temperature Side

The electrical conductivity σ of several samples of olivinites, peridotites, and dunites was measured in the temperature range between 250 and 700°C under quasi‐hydrostatic pressures from 1 to 20 kb. Using a straight line extrapolation of logσ values taken at pressures greater than 6–8 kb, graphs of logσ versus [Formula: see text] were plotted for 0 and 20 kb. These graphs exhibit similar general features to those obtained under room pressure by other authors, but they appear to be shifted towards the low temperature side. This shift may be explained plausibly by assuming much higher values of the preexponential term but only minor variations of the exponential term in the expression [Formula: see text] exp ([Formula: see text]). The electrical conductivity of the samples with high percentage of serpentinized olivine (more than 35 percent) is characterized by a decrease of σ in the temperature interval between 470 and 625°C and is related to the content of serpentine in the samples and its dehydration in this temperature range. Some estimates of temperature within the earth based on conductivity data inferred from magnetotelluric and geomagnetic variation methods are discussed in terms of the present results which suggest substantially lower values of T to be attained at a particular depth. Also, an attempt is made to reexamine assumptions involving the theoretically deduced equation of the electrical conductivity within the earth.

Low-temperature structure of rubrene single crystals grown by vapor transport

2006 ◽  
Vol 62 (2) ◽  
pp. 330-334 ◽  
Author(s):  
Oana D. Jurchescu ◽  
Auke Meetsma ◽  
Thomas T. M. Palstra
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Single Crystals ◽  
Temperature Interval ◽  
Open System ◽  
Vapor Transport ◽  
Entire Temperature Range ◽  
Physical Vapor Transport ◽  
Temperature Structure ◽  
Temperature Range

We report the crystal structure of rubrene, C42H28 (5,6,11,12-tetraphenyltetracene), in the temperature interval 100–300 K. The crystals are grown by physical vapor transport in an open system. The crystal structure is orthorhombic over the entire temperature range.

ABOUT THE CROSSOVER PHENOMENON FOR VRH-CONDUCTIVITY

1994 ◽  
Vol 08 (07) ◽  
pp. 891-896 ◽  
Author(s):  
I.S. Shlimak ◽  
M.J. Lea
Keyword(s):  
Low Temperature ◽  
Fermi Level ◽  
Alternative Explanation ◽  
Temperature Limit ◽  
Activation Process ◽  
The Real ◽  
Temperature Range ◽  
Lower Resistance ◽  
Straight Line ◽  
Increasing Temperature

In a number of recent publications observations of the phenomenon of crossover from the Efros-Shklovskii (ES)-law to the Mott-law in VRH-conductivity were reported. In some experiments, deviations were observed from a straight line in a lnR vs T−1/2 plot to lower resistance values with increasing temperature. However, deviations to higher resistance with increasing temperature should be observed. In other experiments deviations from the “T−1/2 law” to higher resistances with decreasing temperature were observed. This effect was considered as a transition to a simple activation process, “T−1 law”, caused by the appearance of a hard gap at the Fermi level. In the present work an alternative explanation is given, based on the idea that the temperature range showing the “T−1/2 behaviour” actually corresponds to the crossover regime, while the real ES-regime is only reached in the low-temperature limit.

The distribution of minerals in hyper-agpaitic rocks in terms of symmetry: evolution of views on the number and symmetry of minerals

2001 ◽  
pp. 73-82 ◽  
Author(s):  
Alexander P. Khomyakov
Keyword(s):  
Crystal Structures ◽  
21St Century ◽  
Special Interest ◽  
Periodic Table ◽  
Mineral Species ◽  
Original Series ◽  
Temperature Range ◽  
The Earth ◽  
High Alkalinity ◽  
Low Symmetry

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Khomyakov, A. P. (2001). The distribution of minerals in hyper-agpaitic rocks in terms of symmetry: evolution of views on the number and symmetry of minerals. Geology of Greenland Survey Bulletin, 190, 73-82. https://doi.org/10.34194/ggub.v190.5176 _______________ Among the unique mineral localities of the Earth the complexes of nepheline syenites with hyper-agpaitic differentiates are of special interest due to their extreme diversity of mineral species. The four best studied complexes of this type – Khibina, Lovozero, Ilímaussaq and Mont Saint-Hilaire – have yielded more than 700 mineral species of which about 200 are new. The great mineral diversity is due to the combination of several factors, the most important of which is the extremely high alkalinity of agpaitic magmas, causing about half of the elements of the periodic table to be concentrated together. Minerals from hyper-agpaitic rocks are characterised by the predominance of highly ordered, low-symmetry crystal structures resulting, in particular, from the markedly extended temperature range of crystallisation. Generalisation of available data for unique mineral localities underpins the hypothesis that there is no natural limit to the number of mineral species. It is predicted that by the middle of the 21st century, the overall number of minerals recorded in nature will exceed 10 000, with the proportion of triclinic species increasing from the present 9% to 14.5%, and that of cubic species decreasing from 10% to 5%.

MAGNETIC PROPERTIES OF U1-xDyxAlyNi5-y (y=0,1) SYSTEMS

2003 ◽  
Vol 17 (27n28) ◽  
pp. 1453-1460
Author(s):  
ILEANA LUPSA
Keyword(s):  
Magnetic Properties ◽  
Low Temperature ◽  
Spin Fluctuation ◽  
Magnetic Moments ◽  
Transition Temperatures ◽  
Temperature Range ◽  
Fluctuation Model ◽  
Magnetically Ordered

The magnetic properties of U 1-x Dy x Al y Ni 5-y (y=0,1) systems were investigated in the 2(5)–600 K temperature range and for fields up to 80 kOe. The systems having x≥0.2 are magnetically ordered with low transition temperatures and magnetization mainly due to the Dy contribution. The nickel exhibits magnetic moments, very weak in the low temperature range and well-defined effective moments over transition temperatures. The nickel behavior is discussed in terms of the spin fluctuation model.

An Improved Low-Temperature Brittleness Test

1949 ◽  
Vol 22 (3) ◽  
pp. 820-827 ◽  
Author(s):  
E. F. Smith ◽  
G. J. Dienes
Keyword(s):  
Low Temperature ◽  
Temperature Interval ◽  
Statistical Study ◽  
Distribution Curve ◽  
Simple Analysis ◽  
Reasonable Amount ◽  
Brittle Point

Abstract An improved low-temperature brittleness tester, capable of testing five specimens simultaneously, is described. All machine specifications conform to A.S.T.M. Method D 746-44T. Data are presented which show that many elastomers do not possess a sharp brittle point but are characterized by a distribution of failures over a temperature interval. The improved brittleness tester makes it possible to carry out the necessary statistical study of the distribution of per cent failures versus temperature with a reasonable amount of work. A simple analysis of the resulting distribution curve is presented.

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