Order-Disorder Transitions in (CaₓSr₁₋ₓ)₃Rh₄Sn₁₃.

February 22, 2022

In a study published in Physical Review Letters, researchers demonstrated the power of 3D pair distribution function analysis of single-crystal diffuse scattering by analyzing the structural phase transitions in (CaₓSr₁_-ₓ)₃Rh₄Sn₁₃.

Structure of (CaₓSr₁₋ₓ)₃Rh₄Sn₁₃: Tin icosahedra distort on average below structural phase transitions, but 3D-ΔPDF maps of interatomic vectors show that they are still distorted locally at high temperature.
3D-ΔPDF maps: Differences in the probabilities of the tin-tin vectors compared to the average structure. Positive values (red) show that the tin ion displacements from their average positions (blue) do not change with temperature, even above T꜀ = 130K, (b) 30K, (c) 100K, (d) 120K, (e) 150K.

Scientific Achievement

3D-ΔPDF maps show that local atomic distortions are temperature-independent below and above structural phase transitions in quasi-skutterudite compounds, a signature of order-disorder behavior.

Significance and Impact

3D-ΔPDF methods can distinguish ‘order-disorder’ from ‘soft-mode’ phase transitions by analyzing both the average structure and local fluctuations.

Research Details

Single crystal diffuse scattering measurements were performed on (Ca_xSr_1-x)₃Rh₄Sn₁₃, which have structural phase transitions with a quantum critical point at x = 0.9.
The data were transformed into 3D pair distribution functions, using a novel Gaussian filter method that reveals short-range order in real space.
These reveal that the amplitudes of distortions are independent of temperature, below and above T_c.

DOI: 10.1103/PhysRevLett.128.095701

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