One-dimensional behavior of ferroelastic domain arrays in neodymium pentaphosphate

Domain structures in ferroelastic neodymium pentaphosphate NdP₅{O}₁₄$ of small a and b dimensions have been observed to be nearly periodic domain arrays of quasi-one-dimension sandwiched by parallel domain walls along the (001) lattice plane. Based on a continuous order-parameter profile along the wall normal, a positive temperature-dependent wall energy was obtained from Landau's theory of second-order phase transitions. Then a one-dimensional spin system, with the spins corresponding to the shear strains of the two orientation states of NdP₅{O}₁₄$, has been developed to describe statistically the effect of thermal energy exciting the fluctuation of the wall number. The theoretical deductions were well consistent with the actual drastic increase of walls on approaching the phase transition temperature and the dynamical behavior of the domains in external stress fields.