Thermal conductivity, thermopower, and figure of merit ofLa1−xSrxCoO3

Abstract

We present a study of the thermal conductivity κ and the thermopower S of single crystals of La1−xSrxCoO3 with 0 ≤ x ≤ 0.3. For all Sr concentrations La1−xSrxCoO3 has rather low κ values. For the insulators (x < 0.18) this arises from a suppression of the phonon thermal conductivity by lattice disorder due to temperature-and/or doping-induced spin-state transitions of the Co ions. For larger x, the heat transport by phonons remains low, but an additional contribution from mobile charge carriers causes a moderate increase of κ. The thermopower of the low-doped crystals is positive and shows a pronounced maximum as a function of temperature. With increasing x, this maximum strongly broadens and its magnitude decreases. For the highest Sr content (x = 0.3) S becomes even negative in the intermediate temperature range. From S, κ, and the electrical resistivity ρ we derive the thermoelectric figure of merit Z = S 2 / κρ. For intermediate Sr concentrations we find notably large values of Z indicating that Co-based materials could be promising candidates for thermoelectric cooling.

Magnetic and transport properties of the spin-state disordered oxide La0.8Sr0.2CoShibasaki1, Terasaki2, Nishibori3 et al. 2011Phys. Rev. B191120View full textAdd to dashboardCite

“…6 Second, hole-doping drives a spin-state crossover to make Co 3+ ions adopt the intermediate or highspin state and causes various magnetic phases. [7][8][9][10][11][12][13][14] A doped Co 4+ ion dresses a cloud of magnetic Co 3+ ions, as observed by neutron scattering. 15 The double-exchange mechanism between the low-spin Co 4+ (t 2g 5 ) and the intermediatespin Co 3+ (e g 1 t 2g 5 ) stabilizes an itinerant ferromagnetic state in La 1−x Sr x CoO 3 and causes spin-glass or clusterglass behavior depending on the Sr concentration.…”

“…LaCoO 3 -based oxides show fairly good thermoelectric properties at room temperature, 34,35 but the thermopower suddenly decreases to a few μV/K above 500 K, accompanied by a spin-state crossover. [36][37][38] In contrast, LaRhO 3 -based oxides are found to exhibit a large thermopower up to 800 K, 39,40 which is theoretically explained by Usui et al 41 Comparing the transport properties between La 1−x Sr x CoO 3 and La 1−x Sr x RhO 3 , 14,[38][39][40]42 we find three differences as follows: (i) For the same doping level, the resistivity of doped LaCoO 3 is one order of magnitude smaller than that of doped LaRhO 3 .…”

Thermal rectification in bulk materials with asymmetric shape

“…As shown in Fig. 1͑b͒, for LCO and LSCO is five times smaller than that of a single crystal, 20 respectively, which is attributed to the high porosity of the samples. This low thermal conductivity is important to maintain the large Figures 2͑a͒ and 2͑b͒ show the monitored temperatures as a function of time at points ͑1͒-͑4͒ in the forward direction ͑LSCO-top configuration͒ and the reverse direction ͑LCO-top configuration͒, respectively.…”

A Trial Thermal Rectifier

“…LaCoO 3 and La 0.7 Sr 0.3 CoO 3 are good candidate materials for use in such a thermal rectifier for the following reasons: (1) these polycrystalline samples are so dense and hard empirically that the sample is considered to be mechanically strong; (2) the temperature dependences of the thermal conductivities of the two oxides are different, 17 and a rectifying coefficient larger than R = 1.07 reported in the carbon nanotube is expected; and (3) thermal conductivity with a small magnitude ($5 W/m K) compared with that of conventional metals and alloys ($100 W/m K) effectively maintains a large temperature gradient in the system. Because the latter is a characteristic of thermoelectric materials, LaCoO 3 and La 0.7 Sr 0.3 CoO 3 are potential elements for a thermal rectifier.…”