Experiments are reported which show that temperature gradients perpendicular to the surface of epitaxial normal conducting YBa2Cu3O7−δ films give rise to large transversal voltages between contacts on the film surface. The temperature gradients have been produced by pulsed laser irradiation and by continuous heating of the films by heater wires. To explain the large lateral voltages, an atomic layer thermopile is proposed, which may be formed by the layered structure of the material.
Abstract. -Signal pulses of several 100 volts and currents of several amperes have been obtained at lateral surface contacts on normal-state YBa2Cu307_^ films in response to pulsed laser irradiation. The signals are shown to be of thermoelectric origin. Thermoelectric fields transverse to the laser-induced temperature gradient are due to the anisotropy of the thermopower in YB2^Cuz01_i giving rise to non-zero off-diagonal elements a a of the Seebeck tensor for films prepared with a tilt angle a between the film c-axis and the film surface normal. Large-tilt-angle films (up to a = 20°) could be grown on specially cut substrates and may be useful as almost wavelength-independent room temperature radiation detectors. In this letter experiments are reported which proof that the voltaic signals are purely of thermoelectric origin. A comparison of signals induced by laser irradiation, or, alternatively, by a thermal heat source, shows that the signal strength is solely related to the flow of thermal energy through the film. Furthermore, it is shown that the voltaic signals are proportional to the tilt angle a between the crystallographic film c-axis and the film surface normal, in accordance with the tensorial Seebeck effect.The thermoelectric field due to the Seebeck effect is given by where S is the Seebeck tensor and VT the temperature gradient. With respect to the coordinate system defined in fig. 1, the Seebeck tensor for YBa2Cu307_4> depending on the tilt angle a, and taking into account the values of main anisotropy of the thermopower Sc along the crystallographic c-axis and Sab in the (a, 6)-plane [7], is of the form
Articles you may be interested inThe role of a-axis grains in the transition to the normal state of YBa2Cu3O7−δ films and of 2G-coated conductors when induced by high electrical current densities
A synthetic material with large thermoelectric anisotropy has been prepared from a metal–semiconductor multilayer structure. By an alloying process, a multilayer stack A–B–A…, where A and B are pure aluminum and n-silicon, is produced with a thermoelectric anisotropy ΔS=S‖−S⊥≅1.5mV∕K, where S‖ and S⊥ are the absolute Seebeck coefficients along and perpendicular to the layers, respectively. The use of this synthetic material for light sensing applications is demonstrated.
A transverse Peltier effect has been observed in artificially created tilted Pb–Bi2Te3 multilayer structures. Multilayer stacks consisting of alternating layers of Pb and n-type Bi2Te3 have been prepared by a heating procedure and showed large thermoelectric anisotropy up to ΔS≅200μV∕K, depending on thickness ratio p=dBiTe∕dPb, where dBiTe and dPb are the thicknesses of Bi2Te3 and Pb layers, respectively. Tilted samples were obtained by cutting stacks obliquely to the stack axis. Due to large ΔS and large electrical but small heat conductivity, samples showed temperature differences transverse to applied currents up to 22K.
We have measured the thermoelectric response of off-c-axis epitaxial YBa2Cu307 g 6lms with thicknesses between 35 and 500 nm using laser pulses at uv and ir wavelengths. Due to the anisotropy of the thermopower in YBa2Cu30q g, these off-c-axis films show a voltage response proportional to the average temperature gradient in the film which provides a sensitive probe of the temperature distribution within the film. A comparison of the experimental data and calculations with a thermal model for films with different thicknesses, allows us to extract the diffusivity of YBa&Cu307 & and the thermal boundary resistance of the 61m-substrate boundary. Irradiating the films through the substrate leads to a situation where heat How in the interfacial region dominates. The shape of the voltage signals depends strongly on the value assumed for the thermal boundary resistance. A consistent description for both illumination directions is found only in a narrow range around Rqq -0.5 x 10 K cm /W.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.