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Component regulation has a significant influence on the ferroelectric structural phase‐transition characteristics such as the temperature (Tc) and the functional properties. Here, the electrocaloric (EC) properties in potassium tantalate niobate (KTa1−xNbxO3) single crystal are reported. The KTN43 (x = 0.43) single crystal exhibits an adiabatic temperature change of ΔT = 0.76 K at 15 kV cm−1 with both the first‐order and the diffuse phase transition performances near Tc. It represents a good solution for the two intractable contradictions for electrocaloric effect (ECE), namely that the large EC peak value prevents a low working temperature and a wide temperature span. It is shown that improving the Nb component in KTN single crystal can obviously elevate the EC properties. KTN shows good EC properties, including large adiabatic temperature change, low driving electric fields, large refrigeration capacity, working near room temperature and reversibility for all temperature range. These properties indicate that KTN is a promising EC material for practical application.

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The ferroelectric and piezoelectric properties of doped potassium tantalum niobate crystals with different Fe doping amounts and the adjustability of the properties are investigated. The hysteresis loops and current density curves show that the defect dipoles have an obvious effect on domain reorientation, and the effect decreases with increasing doping amount. The ferroelectric and piezoelectric properties can be adjusted via the defect dipoles, and the adjustability is reduced with increasing doping amount. A change of the doping amount leads to defect dipole structure evolution in the crystals, in which the defect dipoles transform from a polar structure to a nonpolar structure, which is the reason for the transition of the domain reorientation determined by the defect dipoles. This result has proved that introducing defects is an effective way to improve and regulate perovskite properties, and the doping amount is one of the important factors controlling the defect dipoles.