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The rapid development of high technology—such as space exploration and electric vehicles—urgently requires ultra-wide temperature multilayer ceramic capacitors (UWT MLCCs) to achieve reliable operation of electronic circuits in harsh environments. However, simultaneously achieving high dielectric permittivity, low dielectric loss, and ultrahigh thermal stability has been a major challenge for practical dielectric ceramics. The co-firing matching of the internal electrode and the dielectric ceramic is also an important factor that affects the reliability of UWT MLCCs. Herein, through multifaceted modification—i.e., composition design related to the modulation of the local polar nanoregions (PNRs) and optimizing device sintering in the context of the compatibility of the heterogeneous interface—these concerns have been well-addressed. A new lead-free dielectric system (1-x) (0.56Na0.5Bi0.5TiO3-0.14K0.5Bi0.5TiO3-0.3NaNbO3)-xCaZrO3 (NKBTNN-xCZ) dominated by P4bm PNRs was designed and corresponding UWT MLCCs with reliable Pt internal electrode interface bonding were fabricated by optimizing the sintering temperature. A record-high dielectric permittivity (er = 839 ± 15 %) and low dielectric loss (tanδ ≤0.02) was achieved over an ultra-wide temperature range from -70 °C to 337 °C for NKBTNN-0.063CZ UWT MLCCs. This work suggests that multifaceted modification should be generalized for construction of high-performance UWT MLCCs.

The assembly of high-temperature electronic equipment places great demands on ultra-high temperature multilayer ceramic capacitors (UHT-MLCCs). However, the relatively low dielectric constant and inferior reliability associated with the protruding ferroelectric phase transition for existing dielectric materials have hindered the development of UHT-MLCCs. Here, these concerns have been addressed by the strategy of composition modulation of different types of polar nanoregions (PNRs) in bismuth-based perovskite relaxor. A new lead-free dielectric system (1-x)(0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xBi(Mg2/3Nb1/3)O3 (NBT-KBT-xBMN) dominated by P4bm PNRs has been built and the corresponding UHT-MLCCs with 70Ag/30Pd inner electrodes are fabricated by tape casting and cofiring processes. A record-high dielectric constant (er = 1800 ± 15%) together with low dielectric loss (tanδ ≤ 0.025) is achieved over a wide range of 100 °C–440 °C for NBT-KBT-0.2BMN MLCC, which consists of nine dielectric layers with the single-layer thickness of 70 μm. The excellent results suggest that NBT-KBT-0.2BMN MLCC can provide realistic solutions for next-generation UHT-MLCC applications and the material design strategy can be generalized for the construction of more high performance capacitor dielectrics.

Grain size effect is one of the most important issues to develop next-generation multilayer microdevices. In this work, the tetragonal 0.4Ba(Zr0.2Ti0.8)O3–0.6(Ba0.7Ca0.3)TiO3 (BZT–60BCT) ceramics with a wide grain size from 2.1 to 24 μm were successfully prepared by using ultrafine nano powder and two-step sintering. The results demonstrate that critical/intermediate grain size of dielectric constant er and piezoelectric constant d33 appears at ∼12.9 μm. It was found that the presence of large lattice tetragonality, and enhanced domain wall motion induced by domain coexistence between submicron and nano size in sample with a grain size of ∼12.9 μm, resulting in the superior dielectric and piezoelectric properties. These findings and analyses of the origin of superior dielectric and piezoelectric properties at intermediate grain size have important practical implications in the design of high-performance piezoelectric ceramics.

Designing piezoceramics with a large transduction coefficient (d33×g33) is key to improving the power generation of piezoelectric energy harvesters (PEHs). However, in popular PEH materials such as Pb(Zn1/3Nb2/3)O3-Pb(Zr1/2Ti1/2)O3 (PZN-PZT), the same trend in the variation of d33 and er makes it difficult to achieve a large d33 × g33. In this work, we introduced low-er Pb(In1/2Nb1/2)O3 (PIN) into the PZN-PZT matrix to pull down the er of the quaternary system. This simultaneously stabilized d33 in a certain range due to the refinement of the domain structure and increased the electrostrictive coefficient (Q33), and consequently the d33 × g33 value increased to 16081 × 10−15 m2/N for the optimal composition. We assembled a cantilever beam type PEH from the preferred material with a power density up to 3.37 μW/mm3 at 1 g acceleration, and demonstrated its use to charge an electrolytic capacitor to drive commercial blue LEDs and a speed sensor.

Tetragonal phase (1–x)(0.875Bi0.5Na0.5TiO3–0.125BaTiO3)–xBi(Mg0.5Ti0.5)O3 lead-free ferroelectrics were designed and fabricated by a conventional solid state route. All the specimens exhibit a tetragonal perovskite structure, and undergo a phase evolution from ferroelectric P4mm to antiferroelectric relaxor P4bm as the BMT addition increases. The critical composition x = 0.04 makes a bridge between the both tetragonal phases, and gives a large field-induced strain of 0.30% and an adequately-large electrostrictive coefficient Q33 of 0.0254 m4/C2. To be highlighted, the field-induce strain of the composition x = 0.04 shows an almost constant value over the temperature range of 18–100 °C, illustrating a temperature-insensitive behavior, which could be attributed to the widened gap between TR–E and TF–R. The temperature-insensitive large strain of the tetragonal BNT–BT–BMT composition give a promising potential for application in precision position actuators.

Piezoelectric energy harvesting is the research hotspot in the field of new energy, and its core is to prepare piezoelectric ceramics with high transduction coefficient ( d 33 × g 33 ) and large mechanical quality factor ( Q m ) as well. In addition, the miniaturization of the piezoelectric energy harvester also requires the material to have a submicron fine grain structure. In this work, submicron-structured ternary system, MnO 2 -doped Pb(Zn 1/3 Nb 2/3 )O 3 -Pb(Zr 0.5 Ti 0.5 )O 3 was constructed by pressureless sintering of nanocrystalline powders, which has been synthesized for the first time by high-energy ball milling route thereby evading the calcination stage. The microstructure and the energy harvesting characteristics were tailored through changing the sintering temperature. It was found that 1000 °C sintered fine-grained specimen (mean grain size ∼0.95 μm) showed the maximum d 33 × g 33 value of 9627 × 10 −15 m 2 /N, meanwhile Q m was as large as 774, which was almost seven times larger than pure counterpart. In the mode of the cantilever-type energy harvester, a high power density of 1.5 μW/mm 3 were obtained for 1000 °C sintered specimen at a low resonance frequency of 90 Hz and acceleration of 10 m/s 2 , which were further increased to 29.2 μW/mm 3 when the acceleration increased to 50 m/s 2 , showing the potential applications as a next generation high power multilayer energy harvester.

Piezoelectric energy harvesting is a hot topic in the field of new energy, and the key point is to design high power lead-free piezoelectric ceramic. In this work, a novel lead–free material system of (1–x)Ba(Zr0.1985Cu0.0015Ti0.8)O3-δ–x(Ba0.7Ca0.3)TiO3 [(1–x)BZCT–xBCT] was designed, and the energy harvesting characteristics were tailored through the composition-driven phase boundary evolution. The R–O–T phase boundary boosts the strong piezoelectric activity, obtaining an optimal energy harvesting performance. In the mode of the cantilever-type energy harvester, a high output power of 70 μW and voltage of 8 V were obtained at x = 0.55 specimen with a low resonance frequency of 90 Hz and acceleration of 10 m/s2, which were further increased to 700 μW and 25 V when the acceleration increased to 50 m/s2. The excellent low frequency characteristics show the potential applications of this material in piezoelectric generators harvesting environmental vibration energy.

The fine-grained xPb(Zn1/3Nb2/3)O3–(1 − x)Pb(Zr0.47Ti0.53)O3 system has been prepared from submicron precursor powders obtained by high-energy ball milling method. The addition of PZN induces a decrease of grain size from an initial micron scale to a submicron scale, accompanying with the phase transition from tetragonal to morphotropic phase boundary (MPB), and then rhombohedral side. Interestingly, compared to the former published data for coarse-grained ceramic, the MPB has shifted from 50% to 30% PZN content side due to the enhancement of the internal stress for fine-grained ceramic. The enhanced electrical and mechanical performances are closely associated with the phase structure and grain size. A high piezoelectric property (d33 = 380 pC/N and kp = 0.49) as well as mechanical performance (Hv = 5.0 GPa and KIC = 1.33 MPa m1/2) were obtained simultaneously for the MPB 0.3PZN–0.7PZT ceramics with an average grain size of 0.65 μm.

A NiO-added Pb((Zn 1/3 Nb 2/3 ) 0.20 (Zr 0.50 Ti 0.50 ) 0.80 )O 3 system is prepared and investigated. The results reveal that Ni doping induces a phase transformation from the morphotropic phase boundary to the tetragonal phase side. Above the solubility limit of 0.3 wt% in NiO form, excess Ni ions segregate at the grain boundaries and triple junctions, which facilitate the formation of a liquid phase with excess PbO and lead to remarkable grain growth. The mechanical behavior (Vickers hardness ( H v ) and fracture toughness ( K IC )) can be tailored by controlling the content of additive; this is accompanied by a transition in the fracture mode changed from transgranular without NiO additive to intergranular with 1.0 wt% NiO additive. Moreover, the NiO addition weakens the dielectric relaxor behavior and improves the piezoelectric properties simultaneously. The 0.2PZN–0.8PZT with 0.5 wt% NiO addition shows good transduction coefficient ( d 33 · g 33 = 10,050 × 10 −15 m 2 /N) and large fracture toughness ( K IC = 1.35 MPa m 1/2 ).

Using the composite powders of (Na 0.5 K 0.5 )NbO 3 (NKN) nano-particles and nano-rods as starting materials, the NKN single crystals were prepared by abnormal grain growth (AGG) method. The morphology evolution and the formation mechanism in the crystal growth process were investigated in detail. The results revealed that the average size and the apparent quantity of abnormal grains increased gradually with the increase of sintering temperature. The biggest NKN single crystals with size of about 3 mm were obtained at 950 °C for 2 h. Though the nano-particles and nano-rods have the same composition, the driving forces are distinctively different due to the diversity of grain morphology. The nano-rods have the large driving forces especially at high sintering temperature, which plays a dominant role in facilitating the formation of NKN single crystals during AGG process.

Lead-free nano (Li0.06Na0.47K0.47)NbO3 powders, with pure perovskite structure and various grain sizes between about 30 and 60 nm, have been successfully synthesized by a novel sol–gel method, in which Nb2O5 was used as the Nb source. The refining XRD and Raman spectra were used in combination with TEM to investigate the evolution of lattice structure and phase transformation behavior as a function of grain size. The results demonstrated that the growth process of grains has been divided into two stages, and the distortion of unit cell apparently decreases with decreasing grain size. At around 35 nm, the phase structure of (Li0.06Na0.47K0.47)NbO3 changed from orthorhombic to tetragonal. This phenomenon is related to a grain size-induced structural phase transition. For the well accepted wisdom that niobates get super piezoelectric properties in orthorhombic–tetragonal transition region, our results suggested a critical size for the application of (Li0.06Na0.47K0.47)NbO3 in nano piezoelectric devices.

The effects of atmospheric powder on microstructure and piezoelectric properties of Pb(Mn1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMZN-PZT) quaternary ceramics were investigated. Specimens with various contents of Pb(Mn1/3Nb2/3)O3 from 0 to 20 mol% were prepared by columbite two-stage process with and without atmospheric powder of PbZrO3. The results revealed that the atmospheric powder is favored to the liquid-state sintering process in PbO vapor pressure equilibrium. The specimen sintered with atmospheric powder is homogenous and the fracture is intergranular. However, the specimen sintered without atmospheric powder is less homogenous and the fracture is essentially transgranular. On the other hand, the pyrochlore phase was formed along with the perovskite phase for the specimens sintered without atmospheric powder and the second phase was seriously detrimental to the electromechanical properties. The superior piezoelectric properties were observed for the specimens sintered with atmospheric powder. By optimizing the specimen composition, excellent piezoelectric, and dielectric properties (Qm=2528, Kp=0.55, tan δ=0.003 ) were obtained at 10 mol% Pb(Mn1/3Nb2/3)O3.