A series of large-sized (maximum 16 × 16 × 20 mm 3 ), high-quality K 1−x Na x NbO 3 (x = 0.118, 0.378, 0.462, 0.545, and 0.666) single crystals were successfully cultivated using the top-seeded solution growth method. The crystallization and structures of the K 1−x Na x NbO 3 single crystals were studied using first-principles calculations and X-ray diffraction, respectively. The segregation of the K 1−x Na x NbO 3 single crystals was investigated, which enabled precise control of the individual components of the crystals during growth. Excellent properties were obtained without annealing, including a low dielectric loss (minimum 0.2%), a saturated hysteresis loop with a low coercive field E c , a large piezoelectric coefficient d 33 (d 33 = 161 pC/N when x = 0.378), and a low leakage current density J (10 −6 A/cm 2 ). These results indicated that the K 1−x Na x NbO 3 (x = 0.118, 0.378, 0.462, 0.545, and 0.666) crystals can be used as a high-quality, lead-free piezoelectric material.

We investigate narrowband transmission filters based on subwavelength-grating reflectors at normal incidence. Computational results show that the filtering is realized through symmetry-protected mode coupling. The guided mode resonances introduced by the slab layer allow flexible control of the filter frequencies. The quality factor of the filters could exceed 106. Dielectric gratings can be used over the entire range of electromagnetic waves, owing to their scale-invariant operations. Owing to the high refraction index and low index dispersion of semiconductors in the infrared range, these filters can be applied over a broad range from near infrared to terahertz frequencies.

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Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (K x Na 1−x )NbO 3 single crystals with an ultrahigh large-signal piezoelectric coefficient d 33 * of 9000 pm V −1 , which is superior to the highest value reported in stateof-the-art lead-based single crystals (~2500 pm V −1 ). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals. , Ultra-large electric field-induced strain in potassium sodium niobate crystals. Sci. Adv. 6, eaay5979 (2020).

A thin radar-infrared stealth-compatible structure with reflectivity below −10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8 µm-14 µm is reported. The designed stealth-compatible structure consists of metallic frequency selective surface (MFSS), resistive frequency selective surface (RFSS), and metal backing from the top down, and it is only 2.1-mm thick. The MFSS is made up of some divided low infrared emissivity metal copper films, and the RFSS consists of a capacitive array of square resistive patches. They are placed close together, working as an admittance sheet because of a mutual influence between them, and the equivalent admittance sheet greatly reduces the thickness of the whole structure. The proposed stealth-compatible structure is verified both by simulations and by experimental results. These results indicate that our proposed stealth-compatible structure has potential applications in stealth fields.

We propose a reflective terahertz (THz) metalens with four focal points for polarization detection of THz beams. The metalens is composed of Z -shaped resonators with spatially variant orientations, a reflective gold layer, and a dielectric spacer between them. The polarization states of the focal points include left circular polarization, right circular polarization, an incident polarization state, and a polarization state whose major axis is rotated π / 4 in comparison with that of the incident polarization. The handedness, ellipticity, and major axis of the polarization state can be determined based on the light intensities of the focal points. The uniqueness of the designed device renders this technique very attractive for applications in compact THz polarization detection and information processing.

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