Effect Of Electroless Plating On Properties Of Bi-Te Based Thermoelectric Materials

With the deterioration of environment and energy problems,the research of new energy conversion materials,such as thermoelectric materials,has attracted widespread attention.Bi-Te based thermoelectric materials are the best thermoelectric materials near room temperature,but there are still some problems,such as low thermoelectric conversion efficiency and poor mechanical properties.In this paper,n-type or p-type Bi-Te based thermoelectric powders were selected as the matrix.The powders were coated with different type and content of metals,and then sintered into bulk.The influence of thermoelectric properties and mechanical properties of materials were studied,specific as follows:1.The effect of Ni content on the properties of p-type Bi_0.5Sb_1.5Te₃/Ni bulk material was studied.The ZT values of all the Bi_0.5Sb_1.5Te₃/Ni samples are basically unchanged or slightly decreased.However,when the Ni content is low,the Seebeck coefficient of the Bi_0.5Sb_1.5Te₃/Ni sample greatly increases,which provides a method for the following experiment.2.The effect of Cu content on the properties of p-type Bi_0.5Sb_1.5Te₃/Cu bulk material was studied.The carrier concentration increases and the carrier mobility decreases with the increasing of Cu content.For all Bi_0.5Sb_1.5Te₃/Cu samples,the electrical conductivity increases and the lattice thermal conductivity has a sharp drop.The thermoelectric properties of the samples were enhanced.At the same time,the ZT peak value shifts to the high temperature with the increase of Cu content.Bi_0.5Sb_1.5Te₃ with 0.05 wt.% Cu bulk sample has the best thermoelectric properties in low temperature zone,the ZT peak value at 372 K increases from _0.59 to 1.08.When the Cu content added to 0.22 wt.%,the ZT peak value moves to high temperature?573 K?and increases from 0.12 to 0.89.3.Based on the results above,we have a thought electroless plating with Ni on the surface of Bi_0.5Sb_1.5Te₃ powders firstly to enhance Seebeck coefficients of the sample,and then electroless plating with Cu to increase the power factor and decrease the thermal conductivity to improve the properties of materials.For all Bi_0.5Sb_1.5Te₃/Ni-Cu samples,the power factor further rises and the lattice thermal conductivity further decreases compared with the Bi_0.5Sb_1.5Te₃/Cu samples.For Bi_0.5Sb_1.5Te₃ with _0.3wt.% Ni and 0.15 wt.% Cu bulk sample,the ZT peak value increases from _0.32 to 1.16 at 473 K,which means the thermoelectric properties of materials have been further ehanced.4.The influence of electroless plating with Cu content on n-type Bi₂Te_2.7Se_0.3/Cu bulk material was investigated.The power factor of Bi₂Te_2.7Se_0.3/Cu samples significantly increases because the Seebeck coefficient greatly increases,which means electrical transport properties of samples have been improved.Similar to Bi_0.5Sb_1.5Te₃/Cu samples,the thermoelectric properties of Bi₂Te_2.7Se_0.3/Cu bulk samples can be enhanced at different temperature range by adjusting the Cu content.Bi₂Te_2.7Se_0.3 with 0.05 wt.% Cu bulk sample has the best thermoelectric properties in high temperature zone,the ZT peak value increases from _0.35 to 0.85 at 623 K.When the Cu content increases to 0.15 wt.%,the ZT peak value moves to the low temperature?373K?and increases from 0.24 to 0.71.At the same time,the mechanical properties of all bulk samples with matal surface modification were improved regardless of the type and content of the metals.