Resistive grain boundary and double-diffused potential barrier formation for delayed dielectric relaxation in SrBi1.98La0.02Nb-TaO9 material

Twin‐Peak Electrocaloric Effect in Ferroelectric Phase of Diffusive SrBi1.98La0.02Nb2−xTaxO9 Materials

“…[ 3,6 ] Previous work establishes the nature of potential barrier formation as well as distribution in samples with x = 0.5 and 1.5 complementary to each other. [ 11 ] Nearly identical Δ S peak positions for the samples with x = 0.5 and 1.5 justify the existence of identical structural distortions with peak height variation largely at the expense of reduced pore width. Heterogeneous applied electric field distribution in these porous structures, e.g., x = 0.5 causes weak spontaneous polarization.…”

“…[1,5,6] In the present case, the sample with x ¼ 1.0 was claimed to contain alternatively distributed close height potential barriers. [11] The switching of dipoles trapped between such repetitive combinations of close barrier height will create similar spontaneous polarization variation as produced by switching between two polar phases near a critical point. This assumption receives support from the work of Qian et al where the production of giant ECE is argued on the basis of switching between different polar states with extremely small energy barriers at electric fields below dielectric breakdown strength.…”

“…In addition to this double peak for ΔS, associated small values can be fairly attributed to the transition between pore-isolated polar domains maintaining orthorhombic phase within a ferroelectric region without involving major structural changes. [3,6,11,17] In the presence of wide pores (width %50 nm and above), the net dipolar contribution and switching are severely affected. [18] In the interior of the material, the external field induces domain-polarization orientation that drives the alignment of dipoles in neighboring domains.…”

“…This is in accordance with earlier work on these materials where the x = 1.0 sample was claimed to exhibit a higher amount of amorphous regions trapped in crystalline networks of similar dimensions. [ 11 ] High thermal stability of SBLNT materials is evident through small values of enthalpy, shown in Figure 2 , the values for fusion and crystallization gradually decrease with increasing Ta content without any shift on a time scale. The high dielectric polarity of metal oxide ceramics is known to attract atmospheric carbonyl and hydroxyl groups.…”

“…Selective SBLNT compounds were prepared by introducing tantalum on B‐site keeping lanthanum‐induced rigid bismuth oxide layer which implicated low porosity, growth of orthorhombic structure, and gradually decreasing phase transition values 683 K, 663 K, 568 K, respectively, for SBLNT ( x = 0.5), SBLNT ( x = 1.0), SBLNT ( x = 1.5) along with rise in diffusivity. [ 11 ] An interesting combination of twin electrocaloric peaks was observed well before Curie temperature in typical SrBi 1.98 La 0.02 Nb‐TaO 9 material due to the matrix exhibiting double‐distributed potential barriers trapping dipoles to undergo dual ECE positive as well as negative. A low‐temperature positive ECE peak that appears near room temperature emerges optimally on increasing Ta content around equal doping stage ( x = 1.0) and pulls the high‐temperature peak significantly toward room temperature.…”