Mid-infrared radiation technique for direct pyroelectric and electrocaloric measurements

A mid-infrared radiometric (MIR) method for precise in situ temperature measurements when studying pyroelectric and electrocaloric properties of bulk and film materials is presented. The method uses new MIR-temperature sensors based on narrowband high-speed and high-sensitive uncooled immersion lens A³B⁵ photodiodes with a precalibration procedure. They are completely insensitive to the background illumination with λ ≤ 1 µm and provide contactless temperature measurements directly in the area of laser heating action. An accuracy of 50 mK at the temperature around 20 °C, rapidly improving up to 1 mK at 200 °C, is achieved at the operation speed of 1 ms. The reliable and reproducible conditions of measurements of pyroelectric and electrocaloric properties of various samples are formulated, and the novel experimental setup is described in detail. The experimental verification of the method is performed by the measurements of pyroelectric properties of single crystals, bulk ceramics, and AlN film. The results of joint measurements of the pyroelectric and electrocaloric properties of the ferroelectric relaxor ceramics are also presented.