Ccente-Olarte, Víctor

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    Caracterización de Cs2CoBr4 y su posible utilización en uniones termoeléctricas
    (2013) Ccente-Olarte, Víctor; Castellano-Rodríguez, Dorial; College of Arts and Science - Science; Méndez-Mella, Héctor; Kim,Yong-Jihn; Department of Physics; Cáceres, Luis R.
    Cs2CoBr4 crystals were grown by the method of fast evaporation. The capacitance of crystals were determined using the LCZ method in the temperature range of 273 K to 310 K and frequency range of 10 KHz to 1 MHz. Graphs of capacitance versus frequency at constant temperature and capacitance versus temperature at constant frequency were constructed. It was found that the crystals undergo a series of phase transitions occurring at a critical temperature of 282 K and 287 K. These transitions correspond to an incommesurate phase transition associated to the Jahn-Teller effect. Strong oscillations observed were due to an induced dipole moment in the crystals which oscillates with the applied external electric field and due to the movement of the ion at position B in the unit cell of the A2BX4 structure. We also measured the thermoelectric properties of Cs2CoBr4 crystals above room temperature using in addition constantan and flux soul wires KH513 from Lincoln Electric. Its average Seebeck coefficient was measured to be ā ≈ 1417.47 μV/K, resistivity was moderate at around ρ ≈ 6818.82x10-2 Ωcm, thermal conductivity k ≈ 7.72x10-7 W/mK, yield η ≈ 0.29182 and figure of merit Z ≈ 3.83x10-3 K-1 for a temperature difference of ΔT ≈ 430 K, where the high temperature was Th ≈ 743 K and the cold temperature Tc ≈ 313 K. According to the spectroscopic X-ray analysis, the material is made up of Cs2CoBr4, Cs3CoBr5, Co6C(CO)12S2, Fe1.874Sn0.096O3 and Ba4In6O13 whose respective crystalline structures were: orthorhombic, tetragonal, monoclinic, hexagonal, and orthorhombic.