Room Temperature Resistivity

The room temperature resistivity q of Tm Se in the homogeneity range of x 0.87 to 1.05 at ambient pressure does not depend strongly on the composition, as shown in the following table according to measurements of Batlogg et al. [2], [3, p. 249] and Haen et al. [1,4]. The 

The conductivity at room temperature increases with increasing pressure with the maximum effect for Tm Se samples nearest the stoichiometric composition, as shown in Fig. 188, Batlogg etal. [3, p. 252]. The pressure dependence for stoichiometric TmSe (a = 5.712 A) is confirmed with an initial decrease of the resistivity of -1.26% per kbar, Ribault et al. [7], see inset in Fig. 193a, p. 370. The change in the resistivity q of nearly stoichiometric TmSe with increasing pressure and literature data on the change of q with increasing nonstoichiometry, both referred to the lattice constants, are shown in Fig. 189, Lapierre et al. [8]. A linear drop of -4.9 fiQ cm kbar between 0 and 43 kbar is reported for a compositionally unspecified sample by Bucher etal. [5, p. 508]. 

conductivity x(co) has been calculated with a Kramers-Kronig analysis from the reflectivity spectrum of stoichiometric TmSe. The real part x (co) for room temperature is shown in Fig. 190. The uncertainty at low frequencies is caused by different extrapolations of the reflectivity. The minimum of x (o)) at -2.6 eV separates the interband from the intraband excitations. x (o)) deviates markedly from a simple Drude model. The d.c. conductivity (x = 4300 -cm 3.9 x10 s i.e., q = 233 fiQ cm) is shown for comparison, Batlogg [9], 

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GMR dramatically en-hanced by presence of the thin Cu layer mag-netoresistance of more than 17% for field changes of 8 kA/ m at room temperature resistance changes as large as 70% within a few tens of amperes per meter... 

Fig. 10. Room temperature resistivity values of PTCR BaTiO samples doped with Y2O2 as a function of mol % Y2O2. Samples were annealed at 1220°C...

The PTCR effect is complex and not fully understood in terms of the grain boundary states and stmcture. Both the PTCR effect and room temperature resistivities are also highly dependent on dopant type and ionic radius. Figure 11 (32) illustrates this dependence where comparison of the PTCR behavior and resistivity are made for near optimum concentrations of La ", Nd ", and ions separately substituted into BaTiO. As seen, lowest dopant concentration and room temperature resistivity are obtained for the larger radius cation (La " ), but thePTCR effect was sharpest for the smallest radius cation (Y " ), reflecting dual site occupancy of the Y " ion. 

Until comparatively recently the bulk of general purpose phthaiate plasticisers have been based on the branched alcohols because of low cost of such raw material. Suitable linear alcohols at comparative prices have become available from petroleum refineries and good all-round plasticisers are produced with the additional advantage of conferring good low-temperature flexibility and high room temperature resistance to plasticised PVC compounds. A typical material (Pliabrac 810) is prepared from a blend of straight chain octyl and decyl alcohols. 

Mineral acids attack the nylons but the rate of attack depends on the type of nylon and the nature and concentration of the acid. Nitric acid is generally active at all concentrations. The nylons have very good resistance to alkalis at room temperature. Resistance to all chemicals is more limited at elevated temperatures. 

Temperature-dependent resistivity data (In p vs 1/T) for both Eu3lnP3 and Eu3ln2P4 are shown in Pig. 11.3 and indicate that they are semiconductors. The room-temperature resistivities are on the order of 1-100 cm. Band gaps were determined by fitting the data from about 130-300 K to the relationship. In p= Eg/ Ik T + f, providing a band gap. Eg, of approximately 0.5 eV for both samples. Since these two compounds can be rationalized as electron-precise Zintl phases, semiconducting behavior is expected. 

The electrical resistivity of the Si-doped quaternary thiospinel, Cus.sSiDi.s Fe4Sni2S32 has been measured, in the temperature range 100 K to 300 K. It was found that it behaves like a semiconductor from room temperature down to 100 K. From the log p ys 1/T plot (see inset of Fig. 15.4) the band gap is found to be 0.107 eV in the temperature range (170 -300 K). The room-temperature resistivity is around 3.1x10 Q-cm (Fig. 15.4). 

Polyesters are, in general, organic solvent resistant. They show excellent room temperature resistance to organic solvents, such as hydrocarbons, alcohols, and chlorinated hydrocarbons. At slightly elevated temperatures of approximately 60 °C, alcohols and aromatic solvents can damage the polymer. Strong acids and bases can cause chemical damage to polyesters, as can ketones and phenols. 

Fig. 17 Room-temperature resistance circle, right axis) and TMR squares, left axis) for variable Alq3 thicknesses. Lines are fits based on (7). Taken from [59] with permission...

Another even more interesting development was occurring at the same time. This was the development of a new growth technique, called the High Temperature Chemical Vapor Deposition (HTCVD) technique [34], that produced crystals that were intrinsically semi-insulating. In a paper by Ellison et al. [34], the authors reported on a defect with an activation energy of 1.15 eV yielding an extrapolated room temperature resistivity in excess of 10 il-cm. 

The ratio of the measured resistance normalized to the room-temperature resistance, (r = R/R0), was found to decrease steadily for NbO until it reached an exceedingly low value at 1.54 K. From these data, they concluded that NbO became superconducting near that temperature. Later authors disagreed, but the most recent results on NbO are in support of that conclusion. 

The changes in resistivity with annealing of films deposited from selenourea and selenosulphate baths, as well as evaporated films, were compared [71,72]. Although there were small differences between the various films, no major difference was found. Additionally, the resistivity of as-deposited films, deposited from both selenourea and selenosulphate baths, does not change with time over a period of months in air. However, after annealing in air at 350°C when the resistivity increases, there is a gradual decrease in room-temperature resistivity (and also in photoconductivity response) with time [73], These variations were related to formation of PbSeOs and adsorbed oxygen on the surface of the annealed crystals. 

The pyrite type of SiP2 forms as black, shiny crystals the cubic cell dimension is a = 5.7045 0.0003 A. The material is stable hydrolytically and is thermally stable in air to 900°C. It is a good metallic conductor with room temperature resistivity of p = 3 X 10 s S2-cm. 

LaOs4Pn is a metal with a room temperature resistivity of about 400 pf2 cm, which decreases to 50 p 2 cm at 2 K followed by superconductivity at 1.8 K (Shirotani et al., 1996 Meisner, 1981). There is a weak decrease of Tc with increasing pressure (Delong and Meis-ner, 1985). 

LaFe4Sbn is a poor metal or heavily doped semiconductor with good thermoelectric properties above room temperature (700-1000 K) (Sales et al., 1996, 1997). Only polycrystalline samples have been investigated. The room temperature resistivity is about 0.5 m 2cm de-... 

Ce[ 64Asi2 is probably a narrow gap semiconductor, but little low temperature data are available for this compound. The resistivity of a polycrystalline sample indicates a small gap on the order of 0.01 eV (Grandjean et al., 1984). The high temperature thermoelectric properties of this compound were investigated by Watcharapasorn et al. (2002). They found semimetallic behavior with a room temperature resistivity of 0.49 m 2 cm, a Seebeck coefficient of 40 pV/K, and a thermal conductivity of 3.8 W/mK. The maximum value for ZT, the thermoelectric figure of merit, was estimated to be 0.4 at 850 K. 

Fig. 9. (a) Scaled resistivity p(T)/p (300 K) vs. T/Tq for YbFe4Sbi2> where Tq is the scaling temperature. Inset shows the pressure dependence of Tq. (b) Scaled resistivity of CeFe4Sbi2 vs. T/Tq. Inset shows pressure dependence of Tq. The room temperature resistivity of both compounds was about 0.8 m cm at ambient pressure (E.D. Bauer et al., 2000). 

The resistivities of the magnetic borides DyB, H0B12, ErB, and TmB, have been carefully measured by Gabani et al. (1999) for good quality crystals with low room temperature resistivities (10-30 p 2 cm) compared to the early work. Near the antiferromagnetic transition temperatures Tn, the resistivities all show small increases in the form of humps and then rapid drops as the temperature is lowered. This behavior can be explained as an initial increase in the resistivity attributed to the appearance of superzone boundaries within the Brillouin zone, followed by a decrease due to a reduction in spin scattering (Taylor and Darby, 1972 Fournier and Gratz, 1993). 

Room temperature resistivities of YB and GdB66 take values of 3 x 102 and 5 x 102 12 cm, respectively (Golikova, 1987) and the RB66 phases can be considered as insulators. The characteristic temperature of the VRH To for example for GdB66 was determined as 4 x 107 K. The conductivity is p-type. The thermal conductivity and thermopower of RB66, will be discussed in Section 12 on "Thermoelectrics in higher borides". 

Fig. 11.10. Room-temperature resistivity of Fe (Si02)i nanocomposite as a function of iron volume fraction.

The non-equilibrium properties of PTC elements can also be utilized. If the room temperature resistance is low there will be a high current surge when a voltage is applied and this will fall to 1% or less of its initial value when the element heats up above its Curie point. Such devices are used in demagnetizing ( degaussing ) coils in T.Y. monitors and in place of capacitors in motor starters. 

The resistivity p of an inductor core material is important because it determines eddy current losses. In general room temperature resistivities of ferrites lie in the range 10 —106Qm, many orders of magnitude higher than that of the most resistive of the ferromagnetic alloys (about 8x10 7 Qm). Typical resistivity-temperature data for MnZn and NiZn ferrites are shown in Fig. 9.22. For both... 

As in WC itself completion of the anion valence shell results in a diamagnetic d2 configuration on the cation of the isomorphous HfS (490). Direct d—d interactions along the c-axis will be responsible if, like WC itself, this compound should turn out to be metallic. McTaggart (92) reports a room-temperature resistivity of 0.5 Q cm for pressed HfS powder which does not exclude semiconductivity. However, according to McTaggart and Wadsley (181) HfS and HfSe are orthorhombic, so probably the stoichiometry of their samples was not 1 1. 

Table I. Room Temperature Resistivities and Thermal Coefficients of Tungsten Bronzes...

Figure 1 shows the overall T dependence of the resistivity in the highly conducting chain direction (pA = I/07,) on a log-log scale for some representative organic metals [14-20]. The points of interest are firstly that ph(T) falls approximately as T1 in all cases except for (TSeT)2Cl, where the dependence is close to T1. Second, the p-(BEDT-TTF)2I3 compound, like others of its family [3], has a particularly large room-temperature resistivity. 

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