The dearth of suitable materials significantly restricts the practical development of infrared (IR) laser systems with highly efficient and broadband tuning. Recently, γ‐NaAsSe2 is reported, and it exhibits a large nonlinear second‐harmonic generation (SHG) coefficient of 590 pm V−1 at 2 µm. However, the crystal growth of γ‐NaAsSe2 is challenging because it undergoes a phase transition to centrosymmetric δ‐NaAsSe2. Herein, the stabilization of non‐centrosymmetric γ‐NaAsSe2 by doping the As site with Sb, which results in γ‐NaAs0.95Sb0.05Se2 is reported. The congruent melting behavior is confirmed by differential thermal analysis with a melting temperature of 450 °C and crystallization temperature of 415 °C. Single crystals with dimensions of 3 mm × 2 mm are successfully obtained via zone refining and the Bridgman method. The purification of the material plays a significant role in crystal growth and results in a bandgap of 1.78 eV and thermal conductivity of 0.79 Wm−1 K−1. The single‐crystal SHG coefficient of γ‐NaAs0.95Sb0.05Se2 exhibits an enormous value of |d11| = 648 ± 74 pm V−1, which is comparable to that of γ‐NaAsSe2 and ≈20× larger than that of AgGaSe2. The bandgap of γ‐NaAs0.95Sb0.05Se2 (1.78 eV) is similar to that of AgGaSe2, thus rendering it highly attractive as a high‐performing nonlinear optical material.
Zn0.64Mg0.36O (ZMO) is a newly discovered ferroelectric oxide with the wurtzite structure. Epitaxial Zn0.64Mg0.36O films from 0.036 to 0.5 μm in thickness are grown on Pt/sapphire with the crystallographic c-axis out of plane. At room temperature, the remanent polarization is ∼80 μC/cm2 and the coercive field is ∼3 MV/cm. The coercive field is strongly temperature dependent up to 240 °C with a pseudo-activation energy of 23 ± 0.3 meV, suggesting that polarization reversal occurs through an extrinsic process such as domain wall motion. ZMO films can be woken up in 20 electric field cycles on driving near the coercive field; they wake up in a single loop at fields in excess of 4 MV/cm. A thermally activated fluid imprint process, with a pseudo-activation energy of 67 ± 8 meV, enlarges the coercive field by several hundred kV cm−1 after switching the polarization. Additionally, ZMO films exhibit excellent retention characteristics; no reduction in the polarization is observed up to 1000 h from room temperature to 200 °C bakes. This current early generation of ZMO films can survive several thousand switching cycles before dielectric breakdown occurs.
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