Zero-Dimensional Molecular Ferroelectrics with Significant Nonlinear Effect and Giant Entropy

Abstract

The search for ferroelectric materials that have a significant progress in applications, such as ferroelectric field-effect transducers, piezoelectric sensors, nonlinear optical devices, electrocaloric refrigeration, and so forth, remains a great challenge. Here, we report the discovery of two unique molecular ferroelectrics (TMP) 2 (SbX 5 )(SbX 3 ) (TMP = thiomorpholine = (CH 2 ) 4 NH 2 S + , X = Cl (1-Cl), Br (2-Br)), which are the first reported examples of halogenoantimonates(III) and halogenobismuthates(III) with R 2 (MX 5 )(MX 3 )-type zero-dimension (0D) configuration ascribing to the discrete SbX 5 and SbX 3 polyhedrons separated by the TMP cations. (TMP) 2 (SbX 5 )(SbX 3 ) also feature the highest phase transition temperature (T c , in which 362/442 K for 1-Cl and 385/477 K for 2-Br) and giant zero-field entropy change (131.68/109.16 J mol −1 K −1 for 1-Cl and 183.24/150.32 J mol −1 K −1 for 2-Br) in halogenoantimonates(III) and halogenobismuthates(III)-based molecular ferroelectrics. A low thr-coordinated SbX 3 component accelerates the crystallization of (TMP) 2 (SbX 5 )(SbX 3 ) in the noncentrosymmetric structure because it breaks the R 2 MX 5 -type construction. Thus, they exhibit significant room-temperature SHG signals (in which 4.2 × KDP for 1-Cl and 3.8 × KDP for 2-Br) and polarization-dependent SHG response. In addition, ultraviolet−visible absorption and photoluminescence spectra reveal that the band gap is successfully tuned from 3.366 to 2.600 eV for 1-Cl to 2-Br, while emission at 545 nm for 1-Cl is redshifted to 611 nm for 2-Br; both large Stokes shifts and broadband emission characterize the PL of 0D metal halide hybrids and are attributed to the strong coupling of the excitons to multiple phonons. This work will provide an avenue to explore the SHG responses and photoelectric characteristics of lowdimensional halogenoantimonates(III) and halogenobismuthates(III)-based molecular ferroelectrics.

Organic Single-Component Enantiomers with High Phase Transition Temperatures and Dielectric Switching Properties

“…The band structures of 1-R and 1-S were calculated according to DFT (Figure S7c–e), and the calculated E g was 5.668/5.658 eV. The experimental energy is relatively higher than the UV–visible absorption edge (5.406/5.504 eV), and this difference stems from the limitations of the DFT method. , Furthermore, we can assign energy bands according to the partial density of states (PDOS) . From the PDOS of 1-R and 1-S in Figure S7d,f, it can be seen that the energy bands at the top of the valence band (VB) originate from the C–P, N–P, and O–P states, whereas the energy band at the bottom of the conduction band (CB) originates from the unoccupied C–P orbital .…”

Nonlinear Optical Glass‐Ceramic From a New Polar Phase‐Transition Organic‐Inorganic Hybrid Crystal

“…The long‐term challenges facing traditional SHG crystals include a high energy‐consuming production process in growing large‐enough single crystals as well as the subsequent difficulty in crystal cuttings or thin‐film fabrication for the inorganic materials, or a poor mechanical strength as well as a low thermal stability for the organic materials [3] . The demands on flexible, easy manufacturing, and highly designable materials have promoted the development of organic–inorganic hybrid crystals, which provide an emerging and promising platform to explore new SHG materials [4–10] …”

“…[3] The demands on flexible, easy manufacturing, and highly designable materials have promoted the development of organic-inorganic hybrid crystals, which provide an emerging and promising platform to explore new SHG materials. [4][5][6][7][8][9][10] The past decade has witnessed the emergence of systematic studies on solid-liquid transitions in hybrid crystals, which provide a novel approach to shape materials with beneficial processability and formability for practical applications. [11][12][13][14] In particular, some hybrid crystals have been proved to form melt-quenched glasses, i.e., hybrid glasses, [15][16][17][18][19][20][21] whose mechanical properties and working temperatures are associated with inner coordination bonds and intermolecular interactions and thus in principle can be tuned by rationally choosing diverse molecular components.…”

Inch-Size Molecular Ferroelectric Crystal with a Large Electromechanical Coupling Factor on Par with Barium Titanate

“…On this account, molecular ferroelectrics have been attracting enormous interest in the last few decades benefiting from their easy fabrication, light weight, satisfactory biocompatibility, and favorable flexibility. − Although numerous molecular ferroelectrics have been reported, − including those with considerably large spontaneous polarization , and high enough Curie temperature, ,, they have suffered from low piezoelectricity for a long time. Until recently, an organic–inorganic perovskite molecular ferroelectric, [Me 3 NCH 2 Cl]­CdCl 3 (TMCM-CdCl 3 ), has been found to exhibit a large d 33 up to 220 pC/N, exceeding that of BTO, which stands out as a promising supplement for inorganic piezoelectric ceramics.…”