Structural, vibrational, and dielectric properties of Ruddlesden-Popper Ba₂ZrO₄ from first principles, by Lydie Louis and Serge Nakhmanson. The picture below shows a tentative sequence of Ba₂ZrO₄ epitaxial phases — determined by evaluating the behavior of low-frequency vibrational modes — depending on the changing biaxial strain ε_s.

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