Effect of donor doping in B sites on the electrocaloric effect of BaTi_1−xNb_xO₃ ceramics

Abstract

This paper demonstrates the effect of donor doping in B sites on the electrocaloric effect (ECE) in BaTi 1-x Nb x O 3 (x=0~0.01) ferroelectric ceramics. The Nb substitution on Ti does not affect the formation of perovskite structure, while it obviously inhabits the grain growth in sintering process. The donor doping of Nb controls the ferroelectric phase transition more efficiently than the equivalent substitutions either in A or B sites. It lowers the phase transition temperature aboutone order of magnitude faster than the equivalent substitution, so that the ECE ∆ ∆ ∆ ∆T max shifts accordingly. Nb doping also diffuses the phase transition, so that the ECE ∆ ∆ ∆ ∆T max reduces and the peak becomes much wider. Compared with BaTiO 3 , ∆ ∆ ∆ ∆T max of BaTi 0.994 Nb 0.006 O 3 drops one third, while the full width at half maximum increases twice, indicating a better refrigeration capacity. a Corresponding author. 3 high ∆T at morphotropic phase boundary [14,15]. In addition, the co-substitution of Ca 2+ on Ba 2+ and Zr 4+ on Ti 4+ was also studied [16-21]. Up to now, all reports focused on the effect of various equivalent dopings but the inequivalent doping has not been researched for ECE, although the inequivalent dopings were reported to improve the dielectric and piezoelectric properties more efficiently [22,23]. The donor doping of Nb 5+ on Ti 4+ in B sites, a typical soft doping, has a notable effect on modifying the ferroelectric phase transition. This paper reports its effects on the phase composition, microstructure, dielectric, ferroelectric and electrocaloric effects of BaTiO 3 ceramics,and a better refrigeration capacity is obtained. Experimental procedure Sample preparationThe BaTi 1-x Nb x O 3 (x=0~0.01) ceramics were prepared by the conventional solid-state reaction method. Analytical reagent grade BaCO 3 , TiO 2 and Nb 2 O 5 were used as raw materials. After the mixed powders were calcined at 1000 °C, they were grinded by planetary ball mill. The resultant powders were dry-pressed in a stainless-steel die under a pressure of 3 MPa and the pressed pellets were sintered at 1350 °C for 4 hours in air. CharacterizationThe phase composition of calcined powders were characterized by X-ray diffraction (XRD) using Cu K α radiation (λ=0.15418 nm) with a scanning rate of 2 °/min. The microstructure of the sintered samples was observed by scanning electron (Figure 2(a)), Nb doped samples exhibit obviously small grain size, less than 1µm, which further decreases with increasing Nb amount (Figure 2 (b)~(d)). It is because the donor doping of Nb accumulates at grain boundaries, which hinders the motion of grain boundaries during the sintering process. The densities of all sintered samples are larger than 5.92 g/cm 3 , i.e. 98% of theoretical density, which well agrees with the SEM observations. Thermal analysisThe thermal characters of tetragonal-cubic (T-C) phase transition are shown in the heat flow curves in Figure 3. With the rise of Nb amount, the endothermic peak gradually moves to lower temperature, indicatin...

Multifunctional barium titanate ceramics via chemical modification tuning phase structure

“…For instance, with increasing the amount of Nb 5+ substitution at B‐site, the ferroelectric‐paraelectric phase transition becomes diffused and moves to low temperature more rapidly than doping by isovalent substitution. After introducing 0.6 mol% Nb 5+ , the highest Δ T of BT ceramic drops to ~0.6 K (under 20 kV/cm) at ~110°C, whereas the full width at half maximum Δ T increases two times 151 …”

“…A and B, ε r ‐ T curves and corresponding Δ T ‐ E curves for pure BT, 148 (Ba 1‐ x Sr x )TiO 3 , 149 (Ba 0.94 RE 0.04 )TiO 3 (RE = rare earth ions), 62 Ba(Ti 1‐ x Zr x )O 3 , 150 and Ba(Ti 1‐ x Nb x )O 3 ceramics 151 . Reproduced with permission 148 .…”

“…Copyright 2018, American Physical Society. Reproduced with permission 151 . Copyright 2015, The Royal Society of Chemistry.…”

“…Copyright 2019, The Royal Society of Chemistry. H and I, Electric field dependence of Δ T near room temperature for BT‐, BNT‐, KNN‐ and Pb‐based ceramics 19,62,138‐146,148‐163 …”

Near‐Room‐Temperature Large Electrocaloric Effect in Barium Titanate Single Crystal Based on the Electric Field–Temperature Phase Diagram

“…It has attracted much attention and become a frontier topic in ferroelectric (FE) scope since the landmark works of giant EC response reported in PbZr 0.95 Ti 0.05 O 3 thin film and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) film. [6,7] The following EC researches involve all kinds of FE material systems (BaTiO 3 , [8][9][10] Pb(ZrTi)O 3 , [11][12][13] BiFeO 3 , [14] Na 0.5 Bi 0.5 TiO 3 , [15][16][17] and (KNa)NbO 3 [18][19][20] ) and sample forms (single crystals, [21][22][23] ceramics, [9,24,25] films, [26][27][28] and multilayer ceramic capacitors (MLCCs) [29][30][31] ). Due to the high polarizability of Pb 2þ , the lead-based FE materials usually exhibit outstanding polarization characteristics, yielding excellent EC effects.…”