fig4

Figure 4. (A) Schematic diagram of lattice softening caused by phase transition; (B) Powder XRD patterns for Bi_2-xSb_xSe₃; (C) Lattice thermal conductivity as a function of the Sb content for Bi_2-xSb_xSe₃. The solid and dashed lines are estimated based on the Klemens-Callaway theory, using different ε values. Copyright 2016, Royal Society of Chemistry^[81]; (D) Grüneisen parameter of β-phase; (E) Grüneisen parameter of α-phase; (F) Experimental and calculated reduction of κ_lat due to reduced speed of sound. Copyright 2024, Wiley^[82]; (G) (Black solid line) Schematic diagram of the temperature dependence of the energy of a typical soft phonon in a second-order phase transition, such as a ferroelectric one. (Red solid line) Soft phonon behavior observed in Ag₈GeSe₆ undergoing a superionic phase transition upon heating. Copyright 2023, the Authors. Small published by Wiley‐VCH GmbH^[84]; (H) E_x as a function of strain ε_xx measured at 4 K on three samples. Inset: Scanning electron micrograph of sample 2; (I) E_x versus ε_xx at a series of temperatures measured on sample 2. Copyright 2023, AAAS^[89]. XRD: X-ray diffraction.