Water-Stable Hybrid Lead-Free Perovskite for Negative Temperature Coefficient Thermistors.

Negative temperature coefficient (NTC) thermistors feature higher sensitivities and faster response speeds and thereby have particular applications in many fields. However, current NTC thermistors are mostly based on inorganic ceramic materials, which show obvious drawbacks in material synthesis, property modulation, and flexible film fabrication. Herein, we report, for the first time, the promising application of an inorganic-organic hybrid NTC thermistor. A new lead-free hybrid iodo bismuthate [1,1',1″-(benzene-1,3,5-triyl)tris(3-methyl-1H-imidazol-3-ium)]Bi2I9 [denoted as (Me3TMP)Bi2I9] was synthesized by a "double-free" strategy. (Me3TMP)Bi2I9 features a lead-free binuclear bismuth iodine anion charge compensated by a "classic hydrogen-bond-free" cation. (Me3TMP)Bi2I9 exhibits remarkable stability in water and UV light irradiation and shows the largest temperature sensitivity coefficient among all reported NTC materials. Theoretical calculation and detailed structural analysis disclose that the seriously distorted (BiI6) octahedra are responsible for the intriguing NTC effect for (Me3TMP)Bi2I9.

Water Stability Studies of Hybrid Iodoargentates Containing N-Alkylated or N-Protonated Structure Directing Agents: Exploring Noncentrosymmetric Hybrid Structures.

In situ alkylation or protonation reactions on the thiazolyl-N donors of benzothiazole (btz) and its derivative 2-aminobenzothiazole (abtz) occurred to form four structure directing agents (SDAs), which feature different structure directing abilities and hydrophobicities. The thiazolyl-N alkylated and protonated btz cations direct to form an α-type (AgI2)- iodoargentate chain in (Etbtz)(AgI2) (1), (Prbtz)(AgI2) (2), and (Hbtz)(AgI2) (3), respectively, while the thiazolyl-N protonated abtz cation directs to form a new type of (Ag2I3)- anionic chain in (Habtz)(Ag2I3) (4). Compounds 1 and 4 represent the first noncentrosymmetric (NCS) hybrid iodoargentates with organic S-containing N-heterocycle derivative cations as SDAs. Further, 1 exhibits high water stability and is second harmonic generation (SHG) active with a response about twice that of KDP (KH2PO4). Importantly, the water stability studies indicate that hybrid iodoargentates with hydrophobic N-alkylated SDAs are more stable in water than those with relative hydrophilic N-protonated SDAs.

A simultaneous disulfide bond cleavage, N,S-bialkylation/N-protonation and self-assembly reaction: syntheses, structures and properties of two hybrid iodoargentates with thiazolyl-based heterocycles.

Solvothermal reactions of AgI with the vulcanization accelerator 2,2'-dibenzothiazolyl disulfide and hydroiodic acid in alcohols afford two hybrid iodoargentates with one-dimensional structures, namely (Et2mbt)[Ag2I3] (1, Hmbt = 2-mercaptobenzothiazole) and {(Hmbt)[AgI]}n (2). The syntheses of both 1 and 2 involve unprecedented multiple in situ reactions. Specifically, a simultaneous disulfide bond cleavage, N and S donor atoms bialkylation, and self-assembly reaction lead to 1 that contains a discrete N,S-biethylated cation (Et2mbt)+ and a rare inorganic (Ag2I3)- anionic chain, while a simultaneous disulfide bond cleavage, N-protonation and self-assembly reaction affords 2 which features zwitterionic Hmbt molecules coordinating with the opposite side Ag atoms of a neutral inorganic (AgI)n chain via forming Ag-S coordination bonds. The simultaneous alkylation on a thiazolyl-N donor and a thiol-S donor atom for a thiazolyl-based heterocycle using inexpensive alcohols and haloids under solvothermal conditions instead of traditional two-step organic synthesis was found for the first time. The two compounds have band gaps of 2.95 eV for 1, and 2.78 eV for 2 exhibiting an observed blue shift compared with bulk AgI. Also, 1 and 2 can be used as effective heterogeneous photocatalysts for methyl orange dye treatment under UV light irradiation.