Dynamics of a Second-Order Phase Transition: P&1macr; to I1 Phase Transition in Anorthite, CaAl2Si2O8

摘要: Electron microscopic study of the reversible P1 to I1 phase transition in anorthite (transition temperature Tc = 516 Kelvin) shows that antiphase boundaries (APBs) with displacement vector R 1/2[111] become unstable at Tc, and numerous small APB loops are formed. These interfaces highly mobile, their vibration frequency increases strongly temperature. observations suggest close breathing-motion—type lattice vibrations framework cause two different configurations around calcium atoms, which related by a translation ≈ 1/2[111], interchange dynamically through an intermediate configuration. The high-temperature structure is interpreted as statistical-dynamic average mobile domains primitive anorthite.