Poly (vinylidene fluoride) (PVDF) is a kind of semicrystalline organic polymer piezoelectric material. Adopting processes such as melting crystallization and solution casting, and undergoing post-treatment processes such as annealing, stretching, and polarization, PVDF films with high crystallinity and high piezoelectric response level can be realized. As a polymer material, PVDF shows excellent mechanical properties, chemical stability and biocompatibility, and is light in weight, easily prepared, which can be designed into miniaturized, chip-shaped and integrated devices. It has a wide range of applications in self-powered equipment such as sensors, nanogenerators and currently is a research hotspot for use as flexible wearable or implantable materials. This article mainly introduces the crystal structures, piezoelectric properties and their applications in flexible piezoelectric devices of PVDF materials.

High-temperature vibration sensors are needed for precise monitoring of dynamic mechanical conditions in aerospace, automotive, and energy-generation-related systems. In this article, a compression-mode vibration sensor was designed and fabricated using a Ba ₂ TiSi ₂ O ₈ single crystal for structural health monitoring at elevated temperatures (650 °C). The fundamental performance of the sensor was simulated, and the effect of pretightening torques on sensor performance was studied. Sensor performance was characterized as a function of temperature up to 650 °C in a frequency range of 100—600 Hz. The sensitivity of the sensor was found to be on the order of 2.6–2.7 pC/g over the tested frequency and temperature ranges, with variation below 2%. In addition, the sensor was found to maintain ultrastable sensitivity at 650 °C. Thus, it exhibits good sensing capability and high reliability at elevated temperatures.

A high-quality Ba₂TiSi₂O₈ (BTS) single crystal was grown using the Czochralski (Cz) pulling method. The thermal expansion and electro-elastic properties of BTS crystal were studied for high temperature sensor applications. The relative dielectric permittivities ${\epsilon }_{11}^T/{\epsilon }_0$ and ${\epsilon }_{33}^T/{\epsilon }_0$ were determined to be 16.3 and 11.8, while the piezoelectric coefficients d_15, d_31, d₃₃ were found to be 17.8, 2.9, and 4.0 pC/N, respectively. Temperature dependence of electro-elastic properties were investigated, where the variation of elastic compliance $s_{55}^E$ (= $s_{44}^E$ ) was found to be 8.5 pC/N) and linear thermal expansion coefficient (8.03 ppm/°C) achieved for BTS crystal along the (47°, φ) direction (φ is arbitrary in 0–360°), together with its good temperature stability up to 650 °C, make BTS crystal a promising candidate for high temperature piezoelectric sensors.

Lithium niobate crystals (LiNbO₃, LN) are multifunctional crystal materials with many outstanding properties. In this work, the electro-elastic properties of LN single crystals were explored at temperatures from −150 °C to 150 °C. The temperature dependences of dielectric permittivities, elastic compliances, electromechanical coupling factors and piezoelectric coefficients were determined using the impedance method. The LN crystals possessed large dielectric permittivities, the ${\epsilon }_{11}^T/{\epsilon }_0$ and ${\epsilon }_{33}^T/{\epsilon }_0$ were 83.2 and 29.4 at room temperature, respectively. The elastic compliances s₁₁, s₁₃, s₃₃ and s₄₄ presented a positive increase as the temperature increased, and the variations were 5.0%, 8.2%, 4.6% and 5.4%, respectively, showing a good temperature stability. Moreover, the temperature dependence of the electromechanical coupling factors and piezoelectric coefficients for different vibration modes were studied with a temperature range from −150 °C to 150 °C, where the thickness shear vibration mode d₁₅ presented a large piezoelectric response and minimal temperature variation.

Pyroelectric properties of orthorhombic Bi₂ZnB₂O₇ (BZBO) crystals were investigated by using the charge integration method. The primary and the secondary pyroelectric coefficients of BZBO crystals were found to be 6.4 and −6.5 µC/(m²·°C), respectively. The pyroelectric performance was evaluated by different figure of merits (FOMs), where BZBO crystals possessed relatively high current responsivity F_i (10.38 pm/V), and detectivity F_d (11.31 × 10⁻⁵/Pa^1/2). In addition, the temperature dependent behaviours of primary pyroelectric coefficients and FOMs were studied from 15 °C to 155 °C; the pyroelectric properties were found to decrease with increases in temperature.