While all of the polymorphs of NH4I and NH4Br are nonpolar, a reversible electric polarization is established in the ordered γ phases of (NH4)0.73(ND4)0.27I and (NH4)0.84(ND4)0.16Br (where D is 2H) via dc electric fields. The presence of two groups of orbital magnetic moments appears to be responsible for the asymmetric lattice distortions. Our findings provide an alternative pathway for hydrogen-based materials to potentially add a ferroelectric functionality.
Yao Li,Siqi Li,Yan Li,Xiangnan Sun,Xinding Lv,Yan-Zhen Zheng,Meilan Huang,Xia Tao
The substitution of a portion of methylammonium (MA) for guanidinium (GA) has been verified to be able to enhance the stability of MA-based devices. However, high-dose guanidinium cation will introduce localized distortions to the perovskite lattice structure and destroy the microstructure of the perovskite films, impairing the stability and reproducibility of perovskite solar cells (PSCs) eventually. Herein, for the first time, the NH 4 Br-assisted all-atmospheric two-step process is adopted to fabricate GA-rich (20%) perovskite films. The NH 4 Br induces the formation of the intermediate phase NH 4 PbI 3 and alleviates the disorder of the octahedron caused by the big GA. Consequently, the modified perovskite film shows increased tolerance for the roughness fluctuation and reduced risk of forming voids and pinholes. The fabricated compact GA-rich perovskite films behave extremely well in photovoltaic performance when assembled as carbon-based perovskite solar cells, delivering a high power conversion efficiency (PCE) of 16.19% and stability against moisture and sunlight. Especially, the unencapsulated devices in ambient air sustain 95.1%, 91.8%, and 95.7% of their initial PCEs after 2400 h of storage, after 1000 h of 65 °C heat environment, and after 800 h of sunlight illumination, respectively.
Different types of magnetism arise mainly from how electrons move and interact with each other. In this work, we show how protons (H+) also exhibit magnetic behavior. We measured the magnetic susceptibility of the ammonium halides and identified pronounced increases at 232, 233, and 243 K for NH4I, NH4Br, and NH4Cl, respectively, all of which coincide with the geometric ordering of their ammonium cations. With extensive literature establishing the fact that the ammonium cations exhibit rotational motion even toward the lowest temperatures, we take into account that the orbital motion of the protons carries a magnetic moment and find it to be larger than that of the paired electrons. Consequently, the structural phase transitions are magnetically driven as the system attempts to lift 8-fold energy degeneracies of the proton orbitals via Jahn–Teller distortions. Our findings identify that NH4+ cations are capable of comprising magnetism which appears to be ubiquitous in ammonia-based molecular solids.
Bin Hu,Wenxuan Hu,Xinyuan Qian,Min Zuo,Ziliang Wu,Yihu Song,Qiang Zheng,Guorong Shan,Miao Du
Layered double hydroxides (LDHs) have garnered significant attention as electrode materials for their ultra-high theoretical capacitance. However, LDHs are prone to phase transition and volume changes during charge/discharge process, which adversely affect their cyclic stability and applications. In this paper, a small amount of non-electrochemically active element, scandium (Sc), was firstly introduced into NiCo-LDHs by a facile and fast one-step potentiostatic electrodeposition with NH 4 Br as a modulator, effectively mitigating the influence of the Jahn-Teller effect. By doping slight Sc into NiCo-LDHs, the resulting electrode exhibited excellent electrochemical performance , with a specific capacitance of 1994 F g −1 (at 1 A g −1 ), and ultralong lifespan, retaining 82.7 % of its initial capacitance after 30,000 charge-discharge cycles. This work presents a promising strategy for the rapid preparation of LDHs-based supercapacitor electrodes that deliver both high specific capacitance and outstanding cycling performance.
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