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Abstract: Dabcodiium chlorochromate chloride was synthesized and separated as crystals. DSC measurement shows that this compound undergoes a reversible phase transition at about 185K with a heat hysteresis of 5K. Step-like dielectric anomaly observed at 187K further confirms the phase transition. The crystal structures determined at 173 and 296K are all monoclinic in P21/m, showing that the phase transition is isosymmetric. The transition is realized by tripling the a-axis without changing the b, c-axes, and β angle. A 60° rotation of one of every three CrO3 groups around the Cr-O bond is probably the driving force of the transition. Hydrogen bonding effect on the transition was shown to be negligible. [Copyright &y& Elsevier]

• High-entropy strategy are proposed to design excellent electrocaloric materials. • The diverse local polar state enhances the macroscopic polarization of PT- x HE. • Dynamics transition of polar nanoregions dominate the mechanism of ECE in PT- x HE. • Optimal Δ T of 1.38 K achieved in PT-0.725HE. • Optimal T span of 116 K achieved in PT-0.775HE. Electrocaloric effect (ECE) materials have garnered significant interest for their potential in creating more portable, compact cooling solutions and reducing greenhouse gas emissions. Enhancing both the temperature change Δ T and the temperature span T span of ECE materials remains a formidable challenge. The diverse and flexible local polarization in the high-entropy ferroelectric materials hold promise for addressing this issue. A series of high-entropy ferroelectric ceramics with composition (1- x)PbTiO 3 - x Pb(Mg 0.2 Zn 0.2 Nb 0.2 Ta 0.2 W 0.2)O 3 has been synthesized using a solid-state reaction. As x increases, the crystal structure transitions towards a cubic phase, and the freezing temperature T f decreases from 92 to 47 °C. There is a notable reduction in the coercive field, and the polarization reaches the maximum value of 32.07 μC/cm2 at x = 0.75. Utilizing the direct method, the samples with x = 0.725 and x = 0.75 achieve an optimal Δ T of 0.35 K and T span of 123 K at an electric field of 20 kV/cm, respectively. The Δ T and T span of the sample with x = 0.75 observed by the indirect method surpass 1 K and 100 K, respectively, at an electric field of 55 kV/cm. This study highlights the potential of employing a high-entropy approach to achieve superior ECE performance, paving the way for the development of advanced cooling technologies. [ABSTRACT FROM AUTHOR]

• High-entropy strategy are proposed to design excellent electrocaloric materials. • The diverse local polar state enhances the macroscopic polarization of PT- x HE. • Dynamics transition of polar nanoregions dominate the mechanism of ECE in PT- x HE. • Optimal Δ T of 1.38 K achieved in PT-0.725HE. • Optimal T span of 116 K achieved in PT-0.775HE. Electrocaloric effect (ECE) materials have garnered significant interest for their potential in creating more portable, compact cooling solutions and reducing greenhouse gas emissions. Enhancing both the temperature change Δ T and the temperature span T span of ECE materials remains a formidable challenge. The diverse and flexible local polarization in the high-entropy ferroelectric materials hold promise for addressing this issue. A series of high-entropy ferroelectric ceramics with composition (1- x)PbTiO 3 - x Pb(Mg 0.2 Zn 0.2 Nb 0.2 Ta 0.2 W 0.2)O 3 has been synthesized using a solid-state reaction. As x increases, the crystal structure transitions towards a cubic phase, and the freezing temperature T f decreases from 92 to 47 °C. There is a notable reduction in the coercive field, and the polarization reaches the maximum value of 32.07 μC/cm2 at x = 0.75. Utilizing the direct method, the samples with x = 0.725 and x = 0.75 achieve an optimal Δ T of 0.35 K and T span of 123 K at an electric field of 20 kV/cm, respectively. The Δ T and T span of the sample with x = 0.75 observed by the indirect method surpass 1 K and 100 K, respectively, at an electric field of 55 kV/cm. This study highlights the potential of employing a high-entropy approach to achieve superior ECE performance, paving the way for the development of advanced cooling technologies. [ABSTRACT FROM AUTHOR]

• The phase transition temperature of Sr 3 Sn 2 O 7 is increased by Ca doping • Ca doping deepens the rotation of oxygen octahedron along the c axis. • The space group of Sr 3 Sn 2 O 7 above 407.9 k is I4/mmm. • Phonon mode A 1 (2) and A 2 (2) are related to the phase transition. The ceramics of Sr 3-x Ca x Sn 2 O 7 (x = 0,0.1,0.2,0.3,0.6,0.8,1) were synthesized by solid-state reaction method. The lattice constants of Sr 3-x Ca x Sn 2 O 7 decrease, and the rotation of oxygen octahedron around c axis increases with the increasing of Ca doping. The phase transition temperature of Sr 3-x Ca x Sn 2 O 7 increases 183.3 K with the increase of Ca doping concentration from × = 0 to × = 0.3. The space group of Sr 3 Sn 2 O 7 changed from A2 1 am to I4/mmm at 407.9 K. Near the phase transition temperature, the Raman shift of phonon mode A 1 (2) of Sr 3-x Ca x Sn 2 O 7 changes abruptly, and the phonon mode A 2 (2) disappears gradually. [ABSTRACT FROM AUTHOR]