Yb-Co-Sb Skutterudite Material with Intergranular Oxide Layer
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Solution Overview
Problem
Thermoelectric conversion materials face challenges in achieving a high dimensionless figure of merit ZT due to the correlation between electrical and thermal conductivity, with materials having high electrical conductivity also having high thermal conductivity, and the introduction of active materials like Ba, La, or Sr reducing reliability and requiring long annealing times.
Innovation Solution
A thermoelectric conversion material with a skutterudite-type crystal structure containing Yb, Co, and Sb, featuring an intergranular layer with an atomic ratio of O to Yb between 0.4 and 1.5, manufactured using a rapid liquid quench method followed by heat treatment and pressure sintering, which increases electrical conductivity while reducing thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active materials like Ba, La, or Sr are introduced to improve thermoelectric performance, then the dimensionless figure of merit ZT increases, but reliability decreases
Solution Approach 1:
The patent changes the chemical composition parameters by using Yb instead of Ba/La/Sr, and controls the oxygen-to-Yb atomic ratio within 0.4-1.5 to prevent excessive oxidation while maintaining thermoelectric performance. This parameter optimization resolves the contradiction between achieving high ZT and maintaining reliability.
Solution Approach 2:
The patent creates a composite structure with an intergranular layer containing Yb and oxygen (forming YbOx with controlled stoichiometry) between the skutterudite grains. This composite approach improves reliability by preventing phase separation while maintaining the thermoelectric properties through the controlled oxide layer.
2Reliability
If conventional annealing methods are used to obtain high-performance thermoelectric material, then ZT increases, but production time increases significantly
Solution Approach 1:
The patent performs preliminary alloying and structural preparation through rapid liquid quenching before the final heat treatment. This preliminary action creates a favorable starting structure that reduces the subsequent annealing time from 168 hours to just 72 hours while achieving the desired thermoelectric performance.
Solution Approach 2:
The patent optimizes the heat treatment parameters (temperature, time, and atmosphere) to achieve the desired microstructure and thermoelectric properties more quickly. By controlling the oxygen-to-Yb ratio and using appropriate heat treatment conditions, the patent reduces processing time while maintaining high ZT values.
3Stability of the object's composition
If Yb2O3 and YbSb2 are produced during annealing, then the material structure changes, but harmful phases are formed
Solution Approach 1:
The patent precisely controls the oxygen-to-Yb atomic ratio to be between 0.4 and 1.5, which prevents the formation of harmful phases like Yb2O3 and YbSb2. By maintaining this specific compositional range, the patent achieves stable skutterudite phase structure without unwanted secondary phases.
Solution Approach 2:
The patent performs heat treatment in an inert or reducing atmosphere to prevent excessive oxidation that would lead to harmful phase formation. This controlled environment maintains the desired phase composition by limiting oxygen availability while still allowing controlled oxide formation in the intergranular regions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a high dimensionless figure of merit ZT and enhances reliability by optimizing the thermoelectric conversion material's conductivity ratios and eliminating the need for long annealing times, making it suitable for mass production.
Implementation Method 1
preparing a ribbon by rapidly cooling and solidifying a melt of the raw materials by using a rapid liquid quench method
Implementation Method 2
heat treating the prepared ribbon in an inert atmosphere with an adjusted oxygen concentration and crushing; second heat treating including heat treating the polycrystalline grains
Implementation Method 3
manufacturing a thermoelectric conversion material by pressure sintering the polycrystalline grains, heat treated in the second heat treating, in an inert atmosphere
Implementation Method 4
When a temperature gradient occurs between one side and the other side of the thermoelectric conversion module, the electrons in the high temperature region are activated in the n-type thermoelectric conversion material, the electrons are diffused to the low temperature region to generate thermoelectromotive force
Data Source
AI summary
A thermoelectric conversion material having a high dimensionless figure of merit ZT includes: a large number of polycrystalline grains which include a skutterudite-type crystal structure containing Yb, Co, and Sb; and an intergranular layer which is between the neighboring polycrystalline grains and includes crystals in which an atomic ratio of O to Yb is more than 0.4 and less than 1.5. A method for manufacturing a thermoelectric conversion material includes: a weighing step; a mixing step; a ribbon preparation step by rapidly cooling and solidifying a melt of the raw materials by using a rapid liquid cooling solidifying method; a first heat treatment step including heat treating in an inert atmosphere with an adjusted oxygen concentration; a second heat treatment step including heat treating in a reducing atmosphere; and manufacturing the thermoelectric conversion material by a pressure sintering step in an inert atmosphere.