A sample-saving method for heat capacity measurements on powders using relaxation calorimetry

Area of Science:

• Materials Science
• Thermodynamics
• Analytical Chemistry

Background:

• Accurate determination of heat capacity (C(p)) is essential for understanding material properties.
• Existing methods for measuring C(p) in small powder samples often lead to contamination, limiting further analysis.
• There is a need for a reliable, non-contaminating method for low-temperature heat capacity measurements of microgram-sized samples.

Purpose of the Study:

• To develop and validate an experimental method for determining the low-temperature heat capacity of microgram-sized powder samples.
• To ensure the method avoids sample contamination, enabling subsequent analyses.
• To achieve high accuracy in heat capacity and entropy measurements for small, precious samples.

Main Methods:

• Utilized a Quantum Design Physical Properties Measurement System (PPMS) for heat capacity measurements.
• Employed differential scanning calorimetry (DSC) for calibration and adjustment of PPMS data.
• Developed a procedure involving compressed powder layers in an aluminum pan without grease, ensuring sample integrity.

Main Results:

• The method demonstrates accuracy better than 1% for heat capacity above 30-50 K and ±3-5% to ±10% below.
• Standard entropy values obtained using this method agree within 0.21%-0.9% with published reference values for various insulating materials.
• The technique provides heat capacity values with less scatter at high temperatures compared to other methods.

Conclusions:

• The described experimental method enables accurate, non-contaminating low-temperature heat capacity and entropy determinations on microgram-sized powder samples.
• This technique is particularly valuable for precious samples available only in limited quantities.
• The high accuracy and sample integrity make this method suitable for further material characterization.