Microstructure and thermoelectric properties of Bi2Te3 electrodeposits plated in nitric and hydrochloric acid baths

Publication date: 1 February 2017
Source:Thin Solid Films, Volume 623
Author(s): Wan-Shan Kang, Wen-Jin Li, Wei-Chen Chou, Mao-Feng Tseng, Chao-Sung Lin
The reduction behaviors of unitary and binary bismuth cation (Bi^III), tellurium cation (Te^IV) in nitric acid and hydrochloric acid solutions were studied at different acid concentrations. Compared to the nitrate bath, the reduction of Bi^III was retarded and the reduction of Te^IV was promoted in hydrochloric acid. As a result, the difference in the reduction potential of Bi^III and Te^IV was markedly reduced in the presence of chloride ion. The acid concentration affected the morphologies of the Bi-Te deposit; specifically a rougher deposit was electroplated at higher acid concentrations. A 25μm Bi2Te3 film obtained from 0.7M HNO3 at −20mV versus saturated calomel electrode (SCE) had columnar structure with (110) preferred orientation and its Seebeck coefficient and power factor were −72.3μV/K and 732μW/m·K², respectively. A 25μm smooth, compact, nano-grained Bi2Te3 film was fabricated in 0.35M HCl at −20mV versus SCE and its Seebeck coefficient and power factor were −105.0μV/K and 169μW/m·K², respectively.