Resistivity anomaly

The atomic mechanism, based on the previously proposed inhomogeneous shear, leading to the formation of twinning and antiphase boundaries in TiNi with the CsCl-type structure is described. The twinning mechanism described herein explains the electrical resistivity anomaly due to incomplete thermal cyclings observed previously in TiNi. This explanation is in keeping, in a qualitative manner, with the "memory effects observed in relation to the electrical resistivity anomaly. 

F or all the highly conducting samples made in this study, care was taken to measure the conductivity quickly after removal from the oven, and to look carefully between 300K and 90K. Generally, no indication of any resistance anomaly was observed, consistent with all previous work in our laboratory. 

These results demonstrate that high temperature resistive anomalies can be produced by temperature dependent contact resistance. Moreover, our experience has been that the contacts can become quite capacitive as the temperature is lowered, shifting the voltage output into quadrature, again producing an apparent drop in resistance. 

Given the fact that resistive anomalies can arise from the above variety of measurement artifacts, we suggest that workers observing indications of... 

The extended resistive bump between 600 C and 800 C can be interpreted similarly. In this case though, the resistive anomaly is pronounced, but the TGA curves only show a slight deviation near 680 C. The resistance curve for Y-Ba Cu Og demonstrates a bump at 750 C which correlates well with tne reported tetragonal to orthorhombic phase transition in Y-Ba Cu O at this temperature (14,15). The corresponding resistance Bump for Er-Ba Cu O indicates that this type of transition also occurs in this compound near this temperature. It is notable that the maximum oxygen uptake in Er- Ba Cu Op at 410 C is below the reported maximum uptake for Y14a2Cu30 sat 500 C. (16)... 

The dependence of our flow-resistance anomalies for HPAA upon salt concentration (Figure 24), is strikingly similar to the salt dependence of pore-flow viscosity enhancement (Figure 18). The critical onset strain rate from our experiments varies in the same way as the critical onset Reynolds number in pore flow. In both experiments no further dependence on salt concentration is observed beyond 0.5 M. Further, in pure water, both experiments show non-Newtonian behavior (in our case identifiable as flare) even at the lowest flow rates. 

Figure 4 is the case of detecting fault fissure water in front of the driving face in Shanxi mine. From the chart, we can see that there is a small and low resistivity anomaly area located near the front of driving face 90 m. After drilling to prove, the location of the 90 m ahead is water point with low... 

It was stressed by Mueller et al. (1980) that the extended Ziman theory is not the only model that can explain the negative value of a observed in many amorphous alloys. In fact, Mueller et al. showed that the negative temperature dependence in amorphous Lao.66 Alo.34 better explained in terms of the Kondo mechanism than by the extended Ziman model. We will return to this point later on, after having discussed the resistivity anomalies associated with several types of Kondo mechanisms. 

Fig. 48. B-T phase diagram of hidden order (HO) phase (I), metamagnetic phase (III) and high field phase (IV). Open symbols correspond to resistivity anomalies and filled symbols to specific heat maxima. For zero field Tq = 17.5 K (HO) (Jaime et al., 2002).

The results of Mackintosh and Spanel (1%4) for Dy in the H a, I c configuration are qualitatively similar to the H b, I c Ho data. The resistance anomaly was used by Akhavan et al. (1973) to determine the temperature dependence of the critical field i/d (see section 2.2.2) to within 1 K of the Neel point. As expected, an approximately linear negative magnetoresistance was observed above... 

Cerium metal is discussed in ch. 4 and only a brief mention of its high pressure behavior will be made here (for references see the list in ch. 4). Cerium can exist at atmospheric pressure in the fee (y) or dhep (iS) form and undergoes an isostructural transition near 100 K to another fcc-form referred to as o-Ce. The y-a Ce transition occurs at 7 kbar at room temperature and this transition is accompanied by about 8% volume decrease. This is one of the most widely studied transitions as a function of pressure and temperature and is believed to involve a valence change from 3 towards a higher valence state (3.7 ). The y to a transition line terminates at a critical point the very first example in which a solid - solid transition was shown to exhibit a liquid-vapor-like critical point. A pressure-induced phase transition near 50 kbar, initially reported to be yet another isostructural transition has been shown to be from fee (a-Ce) to an orthorhombic phase with the a-U structure. Stager and Drickamer (1964) have reported a pronounced resistance anomaly near 120 kbar indicative of a phase transition, but the nature of this transition is unknown. The fusion behavior of Ce is again unique in that it exhibits a minimum. 

Balster and Wittig (1975) detected another anomaly of La which is shown in fig. 10.4. A point of inflection occurs in the R-T characteristic of fee La above 40 kbar. It readily shifts to higher temperatures with pressure. The positions of the points of inflection are shown by the circles in fig. 10.5 which is a hypothetical low-temperature phase diagram. The locus of the points of inflection passes through room-temperature around 70 kbar. This resistance anomaly is not associated with a change of crystal symmetry. Syassen and Holzapfel (1975) found that La has the fee structure between 30 and 120 kbar at room-temperature. It was hence concluded that the points of inflection may indicate the existence of another isostructural phase change whose phase boundary runs into the pressure axis at —25 kbar just where a second kink in Tc(P) occurs for metastable fee La (fig. 10.2). 

Main challenge for application of resistivity methods for surveying contaminated areas is low contrast of anomalies of late and old oil contamination. The problem of distinguishing resistivity anomalies associated with natural properties of soil from anomalies associated with contamination was resolved with the help of petrophysical modeling. 

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