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Negative thermal expansion in ice I polytypes

Leonardo del Rosso, A. Dominic Fortes, Daniele Colognesi, Alberto Santonocito, Francesco Grazzi, Selene Berni, Milva Celli

TL;DR

The paper addresses the metastability and negative thermal expansion of ice I polytypes Ic and Ih. It integrates precise density measurements from neutron diffraction across the metastable range with Path-Integral Molecular Dynamics using the MB-pol(2023) potential to quantify enthalpy differences between Ic and Ih through $\Delta H(T) = H_h(T) - H_c(T)$. The results reveal negative thermal expansion at low temperatures for both polytypes, with Ic having a slightly lower density than Ih at base temperature and transforming to Ih around 200–210 K upon heating; enthalpy differences are negative, confirming Ic as metastable relative to Ih. These findings advance understanding of ice phase thermodynamics and have potential implications for atmospheric, planetary, and remote-sensing contexts where cubicity and density play key roles.

Abstract

The fundamental properties of ice have always attracted a lot of interest due to omnipresence of ice in many different natural contexts. Since cubic ice recently become experimentally accessible from a low-density gas hydrate precursor [1, 2], it has been possible to measure its density as a function of temperature in the whole thermodynamic range of metastability. We found strong analogies with respect to the other ice I polytype, i.e., hexagonal ice Ih [3], including the presence of a negative thermal expansion behavior at low temperature. Based on these results, a new enthalpy calculation quantifies the metastable nature of the cubic form and, consequently its inaccessibility from a "normal" ice Ih precursor.

Negative thermal expansion in ice I polytypes

TL;DR

The paper addresses the metastability and negative thermal expansion of ice I polytypes Ic and Ih. It integrates precise density measurements from neutron diffraction across the metastable range with Path-Integral Molecular Dynamics using the MB-pol(2023) potential to quantify enthalpy differences between Ic and Ih through . The results reveal negative thermal expansion at low temperatures for both polytypes, with Ic having a slightly lower density than Ih at base temperature and transforming to Ih around 200–210 K upon heating; enthalpy differences are negative, confirming Ic as metastable relative to Ih. These findings advance understanding of ice phase thermodynamics and have potential implications for atmospheric, planetary, and remote-sensing contexts where cubicity and density play key roles.

Abstract

The fundamental properties of ice have always attracted a lot of interest due to omnipresence of ice in many different natural contexts. Since cubic ice recently become experimentally accessible from a low-density gas hydrate precursor [1, 2], it has been possible to measure its density as a function of temperature in the whole thermodynamic range of metastability. We found strong analogies with respect to the other ice I polytype, i.e., hexagonal ice Ih [3], including the presence of a negative thermal expansion behavior at low temperature. Based on these results, a new enthalpy calculation quantifies the metastable nature of the cubic form and, consequently its inaccessibility from a "normal" ice Ih precursor.
Paper Structure (6 sections, 3 equations, 3 figures, 1 table)

This paper contains 6 sections, 3 equations, 3 figures, 1 table.

Table of Contents

  1. Main
  2. Methods
  3. Sample synthesis and Raman characterization
  4. Neutron diffraction
  5. Path-Integral Molecular Dynamics Simulations
  6. Thermodynamic Analysis

Figures (3)

  • Figure 1: Representative HRPD diffraction patterns. Ice Ic (top left panel) and ice Ih (bottom left panel) diffraction patterns collected by the back-scattering bank in the 30–130 ms time-of-flight window and measured at 50 K (black crosses) together with Rietveld fits (red lines) plotted against the interplanar spacing (d-spacing). The residuals (blue line) and the positions of the ice Ic (Fd-3m) and Ih (P6$_3$/mmc) reflections (magenta vertical bars) are shown in each panel. In the right panel a 3D stack-plot contains all the diffraction patterns collected by the forward-scattering bank in the 30–130 ms time-of-flight window and measured during the ice Ic-Ih transformation in the temperature range 180 K $\leq T \leq$ 220 K, indicated with labels in the right-side axis.
  • Figure 2: Density of D$_2$O ice I polytypes as a function of temperature. (Top panel) Density of D$_2$O samples for ice Ic and ice Ih (red and blue dots, respectively). The values are obtained by means of Rietveld refinement of the diffraction data (back-scattering bank, 30–130 ms time-of-flight window). For comparison, the density of D$_2$O ice Ih as obtained from synchrotron X-ray Rottger94 and neutron measurements Fortes18 are reported in the plot, with black and green dots, respectively. (Bottom panel) Linear molecular volume expansivity as a function of temperature for ice Ic (red curve) and ice Ih (blue curve) as calculated from the experimental data.
  • Figure 3: Enthalpy jump $\Delta H(T)= H_h(T)-H_c(T)$ for the two ice I polytypes as a function of temperature. Blue empty circles with error bars stand for the present molecular dynamics simulation data on D$_2$O, red empty circle with error bar on H$_2$O, while the red full square with error bar represents the H$_2$O calorimetric measurement from Ref. Tonauer23bis.