Hybrid Improper Ferroelectricity in (Sr,Ca)<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub> and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in <i>n</i> = 2 Ruddlesden–Popper PhasesSuguru Yoshida, Koji Fujita, Ryosuke Tsuji et al.|Journal of the American Chemical Society|2018Cited by 119