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Shift of close-packed basal planes as an order parameter of transitions between antiferromangetic phases in solid oxygen: II. Temperature/pressure dependence of sound velocities and lattice parameters

H. V. Gomonay·V. M. Loktev
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Abstract

In the present paper we generalised a phenomenological model developed in \cite{gomo:2005} for the description of magnetostructural phase transitions and related peculiarities of elastic properties in solid oxygen under high pressure and/or low (below 40 K) temperature. We show that variation of all the lattice parameters in the vicinity of $αβ$-phase transition is due to both the shift of basal closed packed planes and appearance of the long-range magnetic order. Competition between these two factors from one side and lattice compression below $T_{αβ}$ from another produces non monotonic temperature dependence of lattice parameter $b$ (along monoclinic axis). Steep decrease of the sound velocities in the vicinity of $T_{αβ}$ can be explained by the softening of the lattice with respect to shift of the close-packed planes (described by the constant $K_2$) prior to phase transition point. We anticipate an analogous softening of sound velocities in the vicinity of $αδ$-phase transition and non monotonic pressure dependence of sound velocities in $α$-phase.

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H. V. Gomonay, V. M. Loktev. 2007-03-13. Shift of close-packed basal planes as an order parameter of transitions between antiferromangetic phases in solid oxygen: II. Temperature/pressure dependence of sound velocities and lattice parameters. https://arxiv.org/abs/cond-mat/0703350

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