Introduction:

Thermoelectric (TE) materials are one of the best resource of clean energy, which is efficient in conversion of heat energy into electrical energy. There are various applications of TE materials such as electronic component cooling, electricity production from waste heat of automobiles, infrared sensor, etc. The suitability of any materials for TE applications are decided on the basis of their thermoelectric efficiency. This thermoelectric efficiency is defined in terms of a dimensionless parameter called as thermoelectric figure of merit ZT =α2 σT/κ, where α, σ, κ and T are Seebeck coefficient, electrical conductivity, thermal conductivity and absolute temperature, respectively. The square dependent of α in the ZT expression makes it a very important parameter to decide the quality of materials in the TE applications. Therefore I have used the various tools (Experimental and Theoretical) to investigate the temperature dependent thermoelectric properties of various thermoelectric materials in wide temperature range.

Instrumentation: Seebeck coefficient measurement setup in High Temperature range.

In our laboratory we have fabricated a simple and low cost apparatus for the measurement of Seebeck coefficient (α) in the temperature range 300-645 K. Our design is appropriate for the characterization of samples with different geometries like disk and rod shaped. The sample holder assembly of the apparatus has been designed in such a way that, single heater used for sample heating purpose is enough to provide a self maintain temperature gradient (1-10 K) across the sample. The value of α is obtained without explicit measurement of temperature gradient. The whole apparatus is fabricated from the materials, which are commonly available, so that any part can be replaced in case of any damage. A vacuum chamber is fabricated using the Mild steel (MS). This vacuum chamber is capable to hold the vacuum up to 0.001 mbar. The whole sample probe is inserted into the MS vacuum chamber in order to avoid the oxidation of Cu blocks, and it prevents the sample from oxidation and minimize the heat loss due to convective heat exchange.  Labview graphical software is used to interface the Keithley nanovoltmeter 2182A with computer to obtained the data in automated form. Commercially available standard Nickel (Ni) metal sample has been used as a reference material for calibration of the instrument. The experimentally observed value of α by our apparatus gives the similar temperature dependent behavior as reported in the literature.  Although we have used a nanovoltmeter for voltage and digital multimeter for temperature measurement, one can use a microvoltmeter and a simple temperature sensor for the respective measurement. Thus the cost of measurement setup can further be reduced and it will be more cheaper.

Experimental Condensed Matter Physics: Synthesis and Investigation of High Temperature Thermoelectric Materials.

In order to study the thermoelectric behavior of oxide materials, we have synthesized polycrystalline LaCoO3 powder samples by using solution combustion method and investigated the thermoelectric properties. The synthesized powder sample used to make the pallet and sintered it at four different temperature 800, 1000, 1100, 1200 degree Celsius. Crystal structure characterization were done by using the X-ray Diffractometer.  Temperature dependent thermoelectric behavior of these samples were characterized in the temperature range 300-600 K.

Theoretical: Density Functional Theory calculation for investigating the transport properties of thermoelectric materials.

We have used the WIEN2k DFT code to perform the spin polarized calculation on ZnV2O4 compound in Ferromagnetic and Anti-ferromagnetic structure. We have also calculated the density of states as well as dispersion curve.

WIEN2k: The program package WIEN2k allows to perform electronic structure calculations of solids using density functional theory (DFT). It is based on the full-potential (linearized) augmented plane-wave ((L)APW) + local orbitals (lo) method, one among the most accurate schemes for band structure calculations.

To investigate the thermoelectric transport properties we have used Boltztrap code (A code for calculation band-structure dependent quantities). We calculate the temperature dependent Seebeck coefficient for ZnV2O4 compound.


TRAINING/EXPERIENCE:

Sample preparation and characterization:

Laboratory Experience :