Anisotropic thermal expansion of potassium dinitramide: a variable-temperature crystallographic study

Area of Science:

• Crystallography
• Solid-state chemistry
• Materials science

Background:

• Potassium dinitramide (KDN) is an energetic material with potential applications.
• Understanding its thermal expansion properties is crucial for safe handling and application design.
• Previous studies may not have fully characterized its anisotropic thermal behavior.

Purpose of the Study:

• To refine the crystal structure of potassium dinitramide (KDN) across a temperature range.
• To investigate the anisotropic thermal expansion of KDN.
• To analyze the thermal motion of the dinitramide anion using rigid-body analysis.

Main Methods:

• Single-crystal X-ray diffraction data collection from 85-298 K.
• Refinement of unit-cell parameters and atomic positions.
• Analysis of thermal expansion tensor and rigid-body motion (TLS formalism).

Main Results:

• Unit-cell dimensions and volume decrease linearly upon cooling, with the b axis showing the most significant change.
• Thermal expansion is highly anisotropic, with expansion along the [010] direction being over three times greater than other directions.
• Rigid-body analysis indicates anisotropic libration and near-isotropic translation of the dinitramide anion, suggesting anharmonic contributions to the potential.

Conclusions:

• Potassium dinitramide exhibits significant anisotropic thermal expansion, primarily along the b axis.
• The observed thermal motion and expansion are well-described by rigid-body models, with evidence of anharmonicity.
• The findings provide critical insights into the structural behavior of KDN under varying temperatures.