YbAl3 Compound

Title Electrical Resistivity and Seebeck Coefficient of YbAl3 CompoundI prepargond YbAl3 specimens utilizing a hot-pressing technique and so I measured the Seebeck coefficient and galvanising electric vindication oer the temperature scope 150-700K in an private road to measure their possible as thermoelectric stuffs. My consequences show that YbAl3 possesses an electric power factor dual those of the progressive Bi2Te3 thermoelectric stuffs. So I croup reason that YbAl3 is a smart campaigner stuff for thermoelectric coevals utilizing baseborn temperature waste rut.A thermoelectric energy convertor is really alone and dependable hop up engine in which the negatron gas serves as the inventing fluid, BUT, its to a greater ex cristalt wide-scale application has been limited by its comparatively low energy revolution cleverness, so that research attempt has concentrated on bettering its customary unveiling by increasing the thermoelectric -of-merit, Z=a2/rl, of thermocoupl e stuffs, where a is the Seebeck coefficient, r the galvanising electric confrontation, l the thermal conduction a2/r is referred to as the electrical power factor.To day of the month, all the established thermoelectric stuffs ar semiconducting materials in which the thermal conduction consists chiefly of two parts, a lattice and an electronic constituent with the former being importantly the astronomicr of the two. Solid province theory has provided theoretical theoretical accounts of the lattice thermic conduction and oer the past four decennaries research attempts have cerebrate on its decrease. Unfortunately, these attempts have met with limited success due to an attach toing admixture in electrical belongingss ( Rowe and Bhandari 1983 ) . Recently, attending has focused on increasing the electrical power factor and new stuffs, some with fresh constructions such as quantum Wellss ( Mensah and Kanyah 1992, Hicks and Dresselhaus 1993 ) and multiple possible barriers ( Moy zhes and Nemchinsky 1992, Rowe and Min 1994 ) are being proposed in an effort to accomplish this aim.Traditionally, intermetallic compounds are considered inferior thermoelectric stuffs to semiconducting materials because they possess low s-of-merit. However, a member of this household of stuffs is the rare-earth intermetallic compound YbAl3, which exhibits unusual transfer of training belongingss and whitethorn offer possible for development as a high public presentation thermoelectric stuff ( Van Deel et Al. 1974, Mahan and Sofo 1996 ) . The aim of this work is to experience into the thermoelectric belongingss of this promising compound.Specific geometries are commonly necessary in the appraisal of thermoelectric belongingss and stuffs with a comparatively unfit dimension ( over 1 ten 1 ten 1 mm3 ) are normally required in the building of thermoelectric elements. Preparation of such large specimens of pure YbAl3 proved hard due to the peritectic nature of its stage diagram. A lthough good-looking dimension specimens can be prepared utilizing arc-melting technique, stuffs prepared by this method acting are constantly a mixture of YbAl2 and YbAl3 with different proportion depending on the get downing composing and readying conditions. However, pure YbAl3 pulverization can be obtained by crystal growing or solid diffusion ( Rowe et al.1997 ) in an aluminum oxide crucible with extra aluminum utilizing a asseverate flux technique ( Canfield and Fisk 1992 ) . A hot-pressing technique was employed to fix the narrow specimens about 6 millimeters in diameter and 1.5 millimeter midst. Hot-pressing at two hundred MPa was carried out in vacuity ( about 10-2 millimeter of mercury ) and at a temperature of 700 K for approximately 4 hours, followed by a heat intervention at about 900 K in an aluminum purposeless environment for 15 hours. The denseness of the specimen is estimated to be approximately 88 % of its theoretical value. The Seebeck coefficient and elect rical electric resistance as a make up of temperature over the scope 150-700 K were measured simultaneously utilizing an setup draw in ref. ( Rowe et al. 1997 ) .The consequences of the measured Seebeck coefficient and electrical electric resistance are shown in 1 and 2, severally. The corresponding values for the established thermoelectric stuffs Bi2Te3 establish metals ( Yim and Rosi 1972 ) are besides shown in the s for comparing ( broken lines ) . As expected, the electrical electric resistance is much lower than that of Bi2Te3 metal. However, although the Seebeck coefficient of YbAl3 is lower than that of Bi2Te3 based alloys, it is tumesce larger than that of the early(a) intermetallic compounds or metal metals. Consequently, a big electrical power factor is obtained over the whole temperature scope investigated as shown in 3. A maximal a2/r value of about 90 ten 10-4 W/mK2 is obtained at a temperature of around 250 K, which is about twice all bit big as that of the best t hermoelectric stuffs antecedently reported, and over the temperature scope 300-700 K, it exceeds that of Bi2Te3 based metals by at least 50 % .The temperature colony of the Seebeck coefficient for both YbAl3 and Bi2Te3 based alloys appears similar the Seebeck coefficient ab initio increases with an profit in temperature until it reaches a maximal around room temperature and so decreases with a farther addition in temperature. However, the electrical electric resistance of YbAl3 additions with an addition in temperature over the whole temperature scope, while that of Bi2Te3 exhibits a similar tendency as that of the Seebeck coefficient. Bi2Te3 based metals are narrow band-gap semiconducting materials and the temperature dependance of the Seebeck coefficient and electrical electric resistance can be explained within the model of semiconducting material conveyance theory. YbAl3 is a rare-earth intermetallic compound which exhibits unusual electrical belongingss due to the Kondo effec t a lower limit is observed in the temperature dependance of the electrical electric resistance accompanied by a significant value of the Seebeck coefficient. As a consequence, stuffs which exhibit the Kondo effect may possess a significantly big power factor. Furthermore, divergences from the Weidemann-Franz-Lorenz jurisprudence have besides been observed in Kondo materials ( Bauer 1991 ) , which may ease use of the thermic conduction in a similar manner to that in semiconducting materials ( White and Klemens 1992 ) .In drumhead, YbAl3 exhibits a well larger electrical power factor than any other presently available thermoelectric stuffs over the temperature scope 300-500 K. It offers a ordinary advantage for electrical power coevals utilizing waste hot water ( &038 lt 425 K ) , where the electrical power denseness instead than the transition efficiency is a major consideration ( Rowe and Min, 1996 ) . Furthermore, an improved apprehension of its well big electrical power fact or and possible divergence from the Weidemann-Franz-Lorenz jurisprudence may supply an penetration into increasing the thermoelectric -of-merit in other stuffs.This work is supported by the New Energy and Industrial Technology training Organisation ( NEDO ) , the Energy Conversion Centre, Japan. Prof. R.J.D.Tilley, Mr. R. Jones and Dr. D. Pasero are acknowledged for X-ray compend of specimens.Bauer, E. , Adv. Phys. , 40, ( 1991 ) , p417Canfield, P.C. and Fisk, Z. , Philosophical Magazine, 65, 6, ( 1992 ) , p1117Yokels, L.D. and Dresselhaus, M.O. , Phys. Rev. B47, ( 1993 ) , 12 p727Mensah, S.Y. and Kanyah, G.K. , J. Phys Condens. Mater. 4, ( 1992 ) , p919Mahan, G.C. and Sofo, J. O. , Proc. Natl. Acad. Sci. USA, Vol 93, July, ( 1996 ) , p7436Moyzhes, B.Y. and Nemchinsky, V. , Proceedings of 11th International Conference on Thermoelectrics, ( 1992 ) , Arlington, Tx. , USA, p232Rowe, D.M. and Bhardari, C.M. , Modern Thermoelectrics ( Holt, Rinehart and Winston, 1983 )Rowe, D.M. and Mi n, G. , Proceedings of 13th International Conference on Thermoelectric, ( 1994 ) , Kansas City, USA, p339Rowe, D.M. and Min, G. , IEE Pro.-Sci. Meas. Technol. Vol. 143. zero(prenominal) 6. , ( 1996 ) , 351Rowe, D.M. , Min, G. , Williams, S.G.K. , Kuznestsov, V. and Aourn, A. , NEDO Technical Results Report TR3 ( 1996-1997 ) , University of Wales, Cardiff, ( 1997 )Van Daal, H.J. , Van Aken, P.B. and Buschow, K.H.J. , Phys. Lett. , 49A, 3, ( 1974 ) , p246White, D.P. and Klemens, P.G. , J. Appl. Phys. , 71 ( 9 ) , ( 1992 ) , p4258Yim, W.M. and Rosi, F.D. , substantialness Electronics, 15, ( 1972 ) , p1121