Lead telluride materials

In this paper we show how to use a thermodynamic database in a general Calphad approach (3,4) and to understand phases stabilities of diermoelectric materials. Material microstructures after sintering and thermal behavior are checked with the isothennal section at high temperature. Moreover, Gulliver-Scheil simulations (5,6) (infinite diffusion in liquid phase and no diffusion in solid phase) can be used to determine the solid fractions in a solidfication process and the final microstructure. After an example on lead telluride material we will present the features of a general Calphad t proach in thermoelectric antimonides. 

S and p are small in metals, leading to small power factors. On the other hand, S is large for semiconductors or insulators but p is too large, so that S lp is again too small. As shown in Figure 4.3, the maximal value for Z can be obtained for intermediate values of the carrier density, close to 10 —10 cm , typical of semiconductors. Three different families have been traditionally used bismuth-based alloys (BiSb, Bi2Te3...) are used for T ranging from 100 K to 450 K, lead telluride materials are... 

Similar to PbSe, the controlled growth of lead telluride, PbTe, on (111) InP was demonstrated from aqueous, acidic solutions of Pb(II) and Cd(II) nitrate salts and tellurite, at room temperature [13]. The poor epitaxy observed, due to the presence of polycrystalline material, was attributed to the existence of a large lattice mismatch between PbTe and InP (9%) compared to the PbSe/InP system (4.4%). The characterization techniques revealed the absence of planar defects in the PbTe structure, like stacking faults or microtwins, in contrast to II-VI chalcogenides like CdSe. This was related to electronic and structural anomalies. 

Photon detectors consist of a thin film of semiconductor material, such as lead sulfide, lead telluride, indium antimonide, or germanium doped with copper or mercury, deposited on a nonconducting glass and sealed into an evacuated envelope. Photon flux impinging on the semiconductor increases its conductivity. Lead-sulfide detectors are sensitive to radiation below about 3 fj.m in wavelength and have a response time of about 10 /nsec. Doped germanium detectors cooled to liquid-helium temperatures are sensitive to radiation up to about 120 jitm in wavelength, and have a response time of approximately 1 nsec. 

Thermoelectric coolers (TEC) are solid-state heat pumps based upon the Peltier effect without any fluids or moving mechanical parts. In the Peltier effect, a potential is applied to two junctions as shown in Figure 3.15. Heat will be expelled from one junction and absorbed into the other in an amount proportional to the applied current. The thermoelectric cooler consists of an array of junctions using bismuth telluride (Bi2Te3), lead telluride (PbTe), or silicon germanium (SiGe). These materials are doped during fabrication to optimize the parameters of the cooler. Bismuth telluride has been found to have the best performance and is widely used for thermoelectric coolers. 

The next step is to provide electrical connections 3 between the electrode leads 13 and the contact pads 23. Because the active regions are present adjacent the passivated lower surface during the heat treatments, for example when the adhesive layer 4 is cured, they do not suffer significantly from degradation of the material properties of the mercury cadmium telluride... 

Quantum detectors are usually made of semiconductor materials or mixtures. Some commonly used quantum detectors are made of lead sulfide (PbS), lead selenide (PbSe), indium antimony (InSb), or mercury cadmium telluride (MCT, HgTe-CdTe). The absorption of infrared radiation in quantum detectors excites electrons... 

The 3,3 -diaminobenzidine method has been applied for determination of Se in biological materials [28,66], soils [67], air [68], silicates [11], sulphide ores [1], copper [8,14,18], organic substances [69], lead [8,14], steel [29], antimony and bismuth tellurides [70], thin Cd-Se films [71], silver chloride and uranium oxide [12],... 

The dithizone method has been used for determining silver in sewage [12], aluminium and its compounds [51], uranium compounds [52], tin [26], lead [53], gold [54], metal tellurides [55,56], and glass and ceramic materials [57]. 

The chief sources of tellurium at the present time are the slimes from the electrolytic tanks of the copper and lead refineries and the flue dusts from the smelters using certain ores, especially telluride gold ores. It is estimated 1 that the United States alone could produce annually as much as 125,000 pounds of tellurium without making any material additions to the present plants. The amount actually marketed has been small and subject to material variations. No reliable data are available as to the amount sold. 

The ability to control product formation, the reproducibility of results, and the relatively mild conditions under which the reactions proceed, have made cluster syntheses by this method very attractive. Furthermore, the starting materials are themselves readily prepared and easily stored and handled. This is especially valuable in metal telluride chemistry, in which suitable reagents for cluster syntheses are often unstable and must be generated in situ, leading to complex mixtures of reaction products. The use of the silylated tellurium reagents Te(TMS)2 and RTe-TMS has allowed access to a wealth of metal tellurium clusters with unique structures and properties. " ... 

---