Abstract

Molecular dynamics simulations have been performed to investigate the temperature dependence of static and dynamical properties of Na⁺ ions in a one-dimensional tunnel of the hollandite structure. Structural data including the Na⁺ ion distribution obtained from diffraction experiments were well reproduced at room temperature and 773 K. Microscopic pictures and Fourier transforms of the velocity autocorrelation function clarified the diversity in dynamical behavior of Na⁺ ions in a range between 300 and 1273 K. The difference between Ti–Na and Cr–Na pair correlation functions, suggesting the tendency of Na⁺ ions to be closer to Cr³⁺ rather than Ti⁴⁺ in the framework structure, was significant up to at least 1273 K. Correlation of ionic motions is so strong at high temperature as to cause the collective translation of Na⁺ ions in a few tunnels at 773 K and above.