Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

Summary

A protocol for the synthesis and processing of polycrystalline SrTiO₃ ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.

Abstract

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO₃ ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO₃ ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO₃-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO₃.

Introduction

Oxide thermoelectrics were shown to be promising candidates for high-temperature thermoelectric applications, from stability and cost perspectives to electronic transport properties. Among the n-type oxide thermoelectrics, highly doped strontium titanate (STO) has attracted much attention due to its intriguing electronic properties. However, a large total thermal conductivity (κ ~ 12 W m^-1 K^-1 at 300 K for single crystals)¹ and a low carrier mobility (µ ~ 6 cm² V^-1 sec^-1 at 300 K for single crystals)¹ detrimentally affect the thermoelectric performance which is evaluated by a dimens....

Protocol

1. Preparation of Pr-doped SrTiO₃ Powder

1. In order to prepare 10 g of Sr_0.95Pr_0.05TiO₃ powder, weigh the stoichiometric amounts of SrCO₃ powder (7.53407 g), TiO₂ nanopowder (4.28983 g), and Pr₂O₃ sintered lump (0.44299 g) following the reaction for x = 0.05:

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Results

X-ray diffractions patterns were collected for the as-prepared powders and the corresponding bulk ceramics as a function of Pr-content (Figure 1) in order to study the effect of Pr-doping on the SrTiO₃ lattice, solubility of Pr in SrTiO₃ and the formation of secondary phase(s). The patterns confirm the formation of SrTiO₃ phase in all the as-prepared powders where the reflections can be indexed to a cubic lattice with space group (Figure 1A). The monotoni.......

Discussion

In this protocol, we have presented the steps of the synthesis strategy in order to successfully prepare bulk polycrystalline Pr-doped SrTiO₃ ceramics exhibiting improved electronic and thermoelectric properties. The main steps of the protocol include (i) the solid-state synthesis of the doped SrTiO₃ powder in air under atmospheric pressure and (ii) taking advantage of the capabilities of spark plasma sintering technique to densify the as-prepared powder into high-density bulk ceramics and at the sa.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
SrCO3 Powder, 99.9%	Sigma Aldrich	472018
TiO2 Nanopowder, 99.5%	Sigma Aldrich	718467
Pr2O3 Sintered Lumps, 99.9%	Alfa Aesar	35663
Spark Plasma Sintering	Dr. Sinter Lab	SPS-515S
Resistivity/Seebeck Coefficient Measurement System	Ulvac-Riko	ZEM-2
Laser Flash Thermal Diffusivity Measurement System	Netzsch	LFA-457 Microflash
Differential Scanning Calorimetry (DSC) System	Netzsch	404C Pegasus
Physical Property Measurement system (PPMS)	Quantum Design
Field Emission Scanning Electron Microscope (FE-SEM)	Hitachi	SU-6600
Energyy-dispersive X-ray Spectroscopy (EDS)	Oxford Instruments
X-ray Diffractometer	Rigaku	Ultima IV
Bench-top Sputter Coater	Denton Vacuum	Desk II
Diamond  Wheel Saw	South Bay Technology