Electrocaloric effect near room temperature in lead-free Aurivillius phase Sr2Bi4Ti5O18 upon La and Nb codoping

[Description of methods used for collection/generation of data] Crystal structures were characterized by powder X-ray diffraction (XRD) at room temperature in a Rigaku D-Max system using Cu K??1,2 wavelengths. Rietveld analysis of the X-ray patterns was performed using the Fullprof package program. Electrical and electrocaloric properties measurements were conducted on sintered disc-shaped samples, with typical dimensions of 8 mm diameter and thickness between 0.5 and 1 mm. Electrodes were made with silver paste in sandwich geometry. The dielectric constant was derived from measurements with an impedance analyzer (Wayne Kerr Electronics 6500B), applying sinusoidal excitations of 1 V amplitude at several frequencies between 100 Hz and 4 MHz. The polarization versus electric field P(E) curves were recorded using a commercial polarization analyzer (aixACCT Easy Check 300) jointly with a high voltage amplifier (Trek 610E), applying sinusoidal excitations with typical frequency of 10 Hz and E field amplitudes up to 70 kV/cm. Direct measurements of the electrocaloric effect (ECE) were performed using a dedicated in-house-developed quasi-adiabatic calorimeter. The adiabatic temperature change was measured as a function of temperature every 1 K and at different applied E field variations. Samples were measured in the ???contactless??? mode to minimize heat losses, held only by the high voltage coaxial cable and K-type thermocouple for the direct measurement of the temperature variation. Voltages up to either 2 kV or 5 kV were applied using two different homemade high-voltage converters. Heat capacity measurements were also performed, using a commercial adiabatic calorimeter (from Termis Ltd.).