No abstract

Effects of alloying in copper selenide Cu2−xSe with electrically active additions M (where M = In, Sb, In + Sb, Zn, Sn, Zr, Si, Er, Dy, Nd, Al, Cd) are studied in the temperature range of 300 to 430 K which includes the superionic transition temperature (Tc = 413 K for Cu1.998Se) by measuring the modulus of rupture σB, the yeild point σ0.2, the fracture stress ϵB, Young's modulus E, and the microhardness Hμ. It is shown that the doping results in an enhancement of σB, σ0.2, and Hμ and the disappearance of superplasticity at T > Tc.

The data on the fundamental energy gap E in GeTe, g are controversial /1, 2/: the value derived from the optical properties is +s 0.2 eV at 300 K /2h tunnelling studies give 0.2 eV at 4.2 K and 0.1 eV at 300 K /3k from diode laser properties one obtains 0.183 eV at 4.2 K /4/, all of them being much less than thethermalenergygap ((0.75 + 0.25)eV at % 900 K /5/) o r the value 0.9 eV (at 300 K) derived by extrapolation of the E (x) dependence for Pbl -xGexTe alloys with x To explain the difference in Eg for GeTe obtained in /2, 3/ and /5/, Lewis /2/ had used the Boer theory /7/ which predicts a significant rise of the thermal energy gap compared to the optical one in heavily disordered semiconductors. g 0.4 t o x = 1 /6/.The cause of the discrepancy, however, may be different. As is well known, GeTe has three polymorphic modifications /8, 9/. Two of them are low-temperature ones: a rhombohedral a, space group Wm, and an orthorhombic 7 , space group Pnma; one ( fi ) is a high-temperature cubic one, space group FmJm, the p+a( r ) phase transition temperature lying in the interval 630 t o 700 K. The values of E given in /2 to 4/ can be shown /8/ to correspond to a-GeTe, while those in /5/ refer to fi -GeTe, as well as the extrapolatedvalue from /6/ where cubic Pbl -,GeXTe alloys had been investigated /l/. mental energy gaps for various polymorphic modifications of GeTe may be a result of the spontaneous deformation of the GeTe crystal lattice during thep+oc( r ) phase transitions. Three effects accompany the F+a( a ) phase transitions in GeTe / 9 h 1) shear deformation cQL( XY g The present note is intended t o show that a significant difference in the funda-K) 0.015 (0.023) which leads to a splitting of the four 1) Leninskii Prospekt 49, 11 7911 Moscow B-334, USSR.

The placement of thermoelectric generators (TEGs) in vehicles is analyzed, taking into account the interaction of the TEG with the internal combustion engine (ICE). Alternative locations of the TEG directly in the ICE, on the exhaust pipe, and on the cooling system are considered. In all three cases there is a conflict between the two thermal machines, which reduces the total efficiency of the thermodynamic (ICE + TEG) system. It is shown that the cause of the conflict is the low efficiency of the TEG (g TEG < 0.05) compared with that of the ICE (g TEG < 0.4); this conflict increases with the net power W e and decreases with increasing g TEG . For this reason, attainable values of W e , as well as waste heat recovery in cars by the TEG, are significantly limited. Also, some problems of finding materials for automotive TEGs and ways to suppress the parasitic Thomson effect in TEG legs are discussed.

The diagnostic capabilities of the high-speed Harman technique were investigated for measurements of the figure of merit Z in cascade thermoelectric converters with nonuniform legs (inhomogeneous or of an irregular shape). It was shown that, for multistage modules (two stages and more) and for any module with inhomogeneous legs (segmented or graded), the application of the standard Harman technique may lead to incorrect results. Some modifications of the Harman technique are proposed that make it suitable for testing of oneand multistage modules with homogeneous and nonuniform legs.