BaTiO 3 -(Bi 0.5 Na 0.5 )TiO 3 (BTBNT)-based multilayer ceramic capacitor (MLCC) chips with the inner electrodes being Ag0.6/Pd0.4 are prepared by a roll-to-roll casting method. The BTBNT-based MLCC chips with ten-dielectric layers can be sintered very well at a low temperature of 1130°C via two-step sintering (TSS). X-ray diffraction (XRD) and transmission electron microscope (TEM) resultsshow that MLCC chips are a core-shell structure with two phases coexistence.The core exhibits a tetragonal phase at room temperature and then gradually changes into a cubic phase when the temperature increases above T c (175°C).While, the shell exhibits a pseudocubic phase at all tested temperature from 25°C to 500°C. BTBNT-based MLCC chips exhibit a broad temperature stability and meet the requirement of Electronic Industries Association (EIA) X9R specifications. In terms of energy storage performance, a large discharge energy density of 3.33 J/cm 3 can be obtained at 175°C under the applied electric field of 480 kV/ cm. Among all tested temperature ranging from −50°C to 200°C, the energy efficiency of all chips is higher than 80%, even under a high applied electric field.The experimental results indicate that this novel BTBNT-based X9R MLCCs can be one of the most promising candidates for energy storage applications, especially operated in high temperature. K E Y W O R D Score-shell structure, energy storage, multilayer ceramic capacitor (MLCC), two-step sintering (TSS), X9R

We fabricated x(Bi0.5Na0.5)TiO3–(1−x)[BaTiO3–(Bi0.5Na0.5)TiO3–Nb] (BNT‐doped BTBNT‐Nb) dielectric materials with high permittivity and excellent high‐temperature energy storage properties. The initial powder of Nb‐modified BTBNT was first calcined and then modified with different stoichiometric ratios of (Bi0.5Na0.5)TiO3 (BNT). Variable‐temperature X‐ray diffraction (XRD) results showed that the ceramics with a small amount of BNT doping consisted of coexisting tetragonal and pseudocubic phases, which transformed into the pseudocubic phase as the test temperature increased. The results of transmission electron microscopy (TEM) showed that the ceramic grain was the core‐shell structure. The permittivity of the 5 mol% BNT‐doped BTBNT‐Nb ceramic reached up to 2343, meeting the X9R specification. The discharge energy densities of all samples were 1.70‐1.91 J/cm3 at room temperature. The discharge energy densities of all samples fluctuated by only ±5% over the wide temperature range from 25°C to 175°C and ±8% from 25°C to 200°C. The discharge energy density of the 50 mol% BNT‐doped BTBNT‐Nb ceramic was 2.01 J/cm3 at 210 kV/cm and 175°C. The maximum energy efficiencies of all ceramics were up to ~91% at high temperatures and were much better than those at room temperature. The stable dielectric properties within a wide temperature window and excellent high‐temperature energy storage properties of this BNT‐doped BTBNT‐Nb system make it promising to provide candidate materials for multilayer ceramic capacitor applications.

MnO 2 and Nb 2 O 5 co-doped 0.9BaTiO 3 -0.1(Bi 0.5 Na 0.5 )TiO 3 powders with excellent dielectric properties were fabricated using a conventional solid-state reaction method and sand milling. The doping effects of various amounts of MnO 2 on the dielectric properties were investigated. The results revealed that the dielectric properties greatly depended on the concentration of MnO 2 . All the ceramics met the X9R specification. The dielectric loss decreased with an increasing concentration of MnO 2 . The specimen with an appropriate amount of 0.2 mol% MnO 2 exhibited the most enhanced properties: high insulation resistance (2.49 × 10 13 Ω/ cm) and improved degradation properties. Multilayer ceramic capacitor (MLCC) chips were prepared by tape casting using a 0.2 mol% Mn-doped 9010BTBNTbased ceramic powder. The capacitance of the MLCC chip was approximately 100 nF, and the dielectric loss was approximately 1.75% at room temperature.The high-temperature accelerated lifetime was over 1000 hours under 250 V (five times the working voltage) and at 230°C, indicating that the MLCC chips possess superior reliability. K E Y W O R D Score-shell structure, dielectric properties, high-temperature accelerated lifetime test, multilayer ceramic capacitor, tape casting, X9R

Lead-free 0.99(0.96K 0.46 Na 0.54 Nb 1-x Ta x O 3 -0.04Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ZrO 3 )-0.01CaZrO 3 (0.99(0.96KNNTax-0.04BNZ)-0.01CZ) ceramics were prepared by a solid-state sintering method. Ta 2 O 5 doped in the 0.99(0.96KNNTax-0.04BNZ)-0.01CZ ceramics results in a phase structure transition from the orthorhombic (O)/tetragonal (T) phase to the rhombohedral (R)/T phase. The Ta 2 O 5 dopant induces a decrease in the average grain size from~1.70 to~0.69 μm. At x = 0.02 and 0.04, the ceramics have a high reverse piezoelectric coefficient (~500 pm/V under 25 kV/ cm). The ceramics with x = 0.04 show an optimal level of unipolar strain, reaching 0.17% under 35 kV/cm at room temperature, and their field-induced strain varies <10% in the temperature range from 25 to 135°C. The presence of the O phase in the polymorphic phase boundary (PPB) improves the temperature stability the reverse piezoelectric coefficient (d à 33 ). Obtaining KNN-based ceramics with good piezoelectric properties and weak temperature sensitivity by designing a R/O/T phase boundary and controlling the average grain size to the submicrometer level is highly feasible. K E Y W O R D S grain size, lead-free ceramics, phase transition

Lead‐free 0.955K1‐xNaxNbO3‐0.045Bi0.5Na0.5ZrO3+0.4% mol MnO ceramics (Abbreviated as K1‐xNxN‐0.045BNZ+0.4Mn) were prepared by a conventional solid‐state sintering method in a reducing atmosphere (oxygen partial pressure pO2: 1 × 10−11 MPa). All K1‐xNxN‐0.045BNZ+0.4Mn samples show a pure perovskite structure with a polymorphic phase boundary (PPB) composed of rhombohedral (R) and tetragonal (T) phases. A high Na/K ratio and a low Na/K ratio can both induce an increase in the rhombohedral phase. The reverse piezoelectric coefficient d33∗ and its temperature stability in K1‐xNxN‐0.045BNZ+0.4Mn ceramics can be improved by controlling the Na/K ratio. The increase in the Na/K ratio from x = 0.46 to x = 0.56 can decrease the A‐site cation vacancies. The activation energy of the grain is higher than that of the grain boundary due to the accumulation of oxygen vacancies at the grain boundary. K1‐xNxN‐0.045BNZ+0.4Mn ceramics with excellent piezoelectric properties (quasi‐static piezoelectric coefficient d33 = 326 pC/N, and d33∗ = 472 pm/V at Emax = 25 kV/cm) were obtained at x = 0.52.