Hydrogen Bond-Driven Order–Disorder Phase Transition in the Near-Room-Temperature Nonlinear Optical Switch [Ag(NH₃)₂]₂SO₄

Abstract

Herein, we report a near-room-temperature nonlinear optical (NLO) switch material, [Ag(NH 3 ) 2 ] 2 SO 4 , exhibiting switching performance with strong room-temperature second harmonic generation (SHG) intensity that outperforms the UV–vis spectral region industry standard KH 2 PO 4 (1.4 times stronger). [Ag(NH 3 ) 2 ] 2 SO 4 undergoes a reversible phase transition ( T c = 356 K) from the noncentrosymmetric room-temperature phase ( P 4̅2 1 c , RTP) to a centrosymmetric high-temperature phase ( I 4/ mmm , HTP) where both the SO 4 2– anions and [Ag(NH 3 ) 2 ] + cations are highly disordered. The weakening of hydrogen bond interactions in the HTP is also evidenced by the lower energy shift of the stretching vibration of the N–H···O bonds revealed by the in situ FT-IR spectra. Such weakening leads to an unusual negative thermal expansion along the c axis (−3%). In addition, both the atomic displacement parameters of the single-crystal diffraction data and the molecular dynamics-simulated mean squared displacements suggest the motions of the O and N atoms. Such a structural disorder not only hinders the phonon propagation and dramatically drops the thermal conductivity to 0.22 W m –1 K –1 at 361 K but also significantly weakens the optical anisotropy and SHG as verified by the DFT theoretical studies.

Revisiting two thiophosphate compounds constituting d0transition metal HfP2S6and d10transition metal α-Ag4P2S6as multifunctional materials for combining second harmonic generation response and photocurrent response

“…The phase transition from acentric α-Ag 4 P 2 S 6 to centrosymmetric β-Ag 4 P 2 S 6 upon heating is related to a group of emerging functional materials called optical switch. 72–89 In recent years, the optical switch has emerged as a new and important research direction. 72–89 Fig.…”

“…72–89 In recent years, the optical switch has emerged as a new and important research direction. 72–89 Fig. 1b shows the comparison of phase transition temperature between α-Ag 4 P 2 S 6 and many state-of-the-art optical switch materials.…”

“…Increasing the reversibility for inorganic compounds is important for their high temperature applications. 72–89…”

“…The phase transition from acentric α-Ag 4 P 2 S 6 to centrosymmetric β-Ag 4 P 2 S 6 upon heating is related to a group of emerging functional materials called optical switch. [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] In recent years, the optical switch has emerged as a new and important research direction. [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] Fig.…”

“…[72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] In recent years, the optical switch has emerged as a new and important research direction. [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] Fig. 1b shows the comparison of phase transition temperature between α-Ag 4 P 2 S 6 and many state-of-the-art optical switch materials.…”