Dielectric energy-storage capacitors have received increasing attention in recent years due to the advantages of high voltage, high power density, and fast charge/discharge rates. Here, a new environment-friendly 0.76NaNbO 3 -0.24(Bi 0.5 Na 0.5 )TiO 3 relaxor antiferroelectric (AFE) bulk ceramic is studied, where local orthorhombic Pnma symmetry (R phase) and nanodomains are observed based on high-resolution transmission electron microscopy, selected area electron diffraction, and in/ex situ synchrotron X-ray diffraction. The orthorhombic AFE R phase and relaxor characteristics synergistically contribute to the record-high energy-storage density W rec of ≈12.2 J cm −3 and acceptable energy efficiency η ≈ 69% at 68 kV mm −1 , showing great advantages over currently reported bulk dielectric ceramics. In comparison with normal AFEs, the existence of large random fields in the relaxor AFE matrix and intrinsically high breakdown strength of NaNbO 3 -based compositions are thought to be responsible for the observed energy-storage performances. Together with the good thermal stability of W rec (>7.4 J cm −3 ) and η (>73%) values at 45 kV mm −1 up to temperature of 200 °C, it is demonstrated that NaNbO 3 -based relaxor AFE ceramics will be potential lead-free dielectric materials for next-generation pulsed power capacitor applications.

It has been reported that the rhombohedral–orthorhombic low‐temperature polymorphic phase transition in (Na,K)NbO3 can be tuned close to room temperature by substituting Sb for Nb, such that enhanced piezoelectric properties are induced based on the theory of two‐phase coexistence. A diagram of phase structures changing with Sb content and temperature has been generalized for (Na,K)(Nb,Sb)O3 (NKNS) compositions. The thermal stability of piezoelectric properties of NKNS ceramics was evaluated considering the existence of successive phase transition above room temperature. The microstructure, dielectric, and ferroelectric properties of NKNS ceramics were discussed from a crystallographic point of view.

The phase transitional behavior and composition‐dependent piezoelectric properties of (NaK)(NbSb)O3–LiTaO3–BaZrO3 (NKNS–LT–BZ) pseudo‐ternary system were investigated. A composition–temperature phase diagram was generalized within a certain range of BZ content in which a rhombohedral–tetragonal (R–T ) ferroelectric phase boundary connecting orthorhombic and cubic phase zones is formed near room temperature between two trifurcate points. Piezoelectric and electromechanical properties of NKNS–LT–BZ ceramics exhibit optimum values of d33=365 pC/N and kp=45% in the vicinity of the R–T phase coexistence zone. The dielectric and ferroelectric properties and the phase transition of NKNS–LT–BZ ceramics were discussed from a crystallographic point of view.

Lead-free (Na 0.52 K 0.48Àx )(Nb 1ÀxÀy Sb y )O 3 -xLiTaO 3 (NKNS-LT) piezoelectric ceramics have been fabricated by ordinary sintering. A special attention was paid to the composition design through which the dielectric and piezoelectric properties of the (Li, Ta, Sb) modified NKN systems were significantly promoted. A property spectrum was generated with a particular discussion on the relationship between the Sb content, the LT content, the polymorphic phase transition, and the electrical properties and their temperature stability. Excellent and tunable electrical properties of d 33 5 242-400 pC/N, k p 5 36%-54%, e 33 T ¼ 750À 2500, and T c 5 2301-4301C demonstrate a tremendous potential of the compositions studied for device applications.

The origin of high piezoelectric response in (Na0.52K0.48−x)(Nb0.92−xSb0.08)O3-xLiTaO3 lead-free ceramics was investigated by looking into the composition-dependent domain morphology by means of transmission electron microscopy. Nanodomains of alternate orthorhombic and tetragonal domains with a width of 20–50 nm were surprisingly observed but only for compositions near polymorphic phase coexistence zone. The formation of nanodomain morphology was considered to result from the reduction of the domain wall energy owing to the vanishing of the polar anisotropy, which ultimately induced enhanced piezoelectric properties. The result indicated that nanodomains are not proprietary features of traditional Pb-based piezoelectric ceramics with a morphotropic phase boundary.