Influence of isotopic disorder on solid state amorphization and polyamorphism in solid ${\mathrm{H}}_2\mathrm{O}-{\mathrm{D}}_2\mathrm{O}$ solutions

We present a low-temperature and high-pressure ultrasonic study of elastic properties of isotopic ${\mathrm{H}}_2\text{O-}{\mathrm{D}}_2\mathrm{O}$ solid solutions, comparing their properties with those of the isotopically pure ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$ ices. Measurements were carried out for solid state amorphization (SSA) from 1h to high-density amorphous (HDA) ice upon compression up to 1.8 GPa at 77 K and for the temperature-induced $(77-190\mathrm{K})$ u-HDA (unrelaxed HDA) → e-HDA (expanded HDA) → low-density amorphous $\left(\mathrm{LDA}\right)\to 1\mathrm{c}$ cascade of ice transformations near room pressure. There are many similarities in the elasticity behaviour of ${\mathrm{H}}_2\mathrm{O},{\mathrm{D}}_2\mathrm{O}$, and ${\mathrm{H}}_2\text{O-}{\mathrm{D}}_2\mathrm{O}$ solid solutions, including the softening of the shear elastic modulus as a precursor of SSA and the $\mathrm{HDA}\to \mathrm{LDA}$ transition. We have found significant isotopic effects during H/D substitution, including elastic softening of ${\mathrm{H}}_2\mathrm{O}-{\mathrm{D}}_2\mathrm{O}$ solid solutions with respect to the isotopically pure ices in the case of the bulk moduli of ices 1c and 1h and for both bulk and shear elastic moduli of HDA ice at high pressures $(>1\mathrm{GPa})$. This softening is related to the configurational isotopic disorder in the solid solutions. At low pressures, the isotope concentration dependence of the elastic moduli of u-HDA ice changes remarkably and becomes monotonic with pronounced change of the bulk modulus $(\approx 20\%)$.

Figure 1

Pressure dependences of the longitudinal and transverse sound velocities for the SSA of ice 1h at 77 K. Solid symbols correspond to compression, open to decompression solid solutions. Solid lines correspond to pure ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$.

Figure 2

Pressure dependences of the relative volume and bulk and shear elastic moduli for the SSA of ice 1h at 77 K. Solid symbols correspond to compression, open to decompression solid solutions. Solid lines correspond to pure ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$.

Figure 3

Concentration dependences of pressure derivatives of bulk and shear elastic moduli of ice 1h at 77 K and $\mathrm{P}=0$. The dashed line in the top panel is approximation by second-order polynomial. The dashed-dotted line in the bottom panel is guide for ice.

Figure 4

The concentration dependences of the bulk and shear elastic moduli and their pressure derivatives of u-HDA ice at 77 K and 1.6 GPa. The dashed lines are approximations by second-order polynomials.

Figure 5

Temperature dependences of the relative volume and transverse and longitudinal sound velocities for the temperature-induced transitions at 0.05 GPa with the identification of various transition stages. Solid lines correspond to pure ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$. The dark cyan arrows correspond to the possible values of the glass transition temperature according to the Refs [15] and [16].

Figure 6

Temperature dependences of bulk and shear elastic moduli for the temperature-induced transitions at 0.05 GPa. The identification of transition stages is the same as in Fig. 5. Solid lines correspond to pure ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$.

Figure 7

The concentration dependences of bulk and shear moduli of the u-HDA ice at 90 K and bulk modulus of ice 1c at 165 K $(P=0.05\mathrm{GPa})$.