New Molecular Ferroelectrics Accompanied by Ultrahigh Second-Harmonic Generation

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• 作者：Chuang Liu ; Kaige Gao ; Zepeng Cui ; Linsong Gao ; Da-Wei Fu ; Hong-Ling Cai ; X. S. Wu
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：May 19, 2016
• 年：2016
• 卷：7
• 期：10
• 页码：1756-1762
• 全文大小：431K
• 年卷期：0
• ISSN：1948-7185

文摘

Second-harmonic generation (SHG) is one of the outstanding properties for practical applications. However, the great majority of molecular ferroelectric materials have very low nonlinear optical coefficients, attenuating their attractive performance. Here we synthesized (4-amino-2-bromopyridinium)(4-amino-2-bromopyridine)tetrafluoroborate (1), whose second-order nonlinear optical coefficient reaches up to 2.56 pm V^–1, 2.67 times of that of KDP, and (4-amino-2-bromopyridinium)tetrafluoroborate (2), possessing a more incredible large second-order nonlinear optical coefficient as high as 10.24 pm V^–1, 10.67 times that of KDP. The compound 1 undergoes two reversible phase transitions at around T₁ = 244.1 K and T₂ = 154.6 K, caused by dramatic changes of the protonated cations and order–disorder of anions, which was disclosed by differential scanning calorimetry, heat capacity, dielectric anomalies, SHG, and single-crystal X-ray diffraction analysis. The pyroelectric measurements reveal that compound 1 is a Rochelle salt type ferroelectric, which has a large spontaneous polarization of about 3 μC/cm².