On the possibility that PbZrO3 not be antiferroelectric

Lead zirconate (PbZrO3) is considered the prototypical antiferroelectric material with an antipolar ground state. Yet, several experimental and theoretical works hint at a partially polar behaviour in this compound, indicating that the polarization may not be completely compensated. In this work, we propose a simple ferrielectric structure for lead zirconate. First-principles calculations reveal this state to be more stable than the commonly accepted antiferroelectric phase at low temperatures, possibly up to room temperature, suggesting that PbZrO3 may not be antiferroelectric at ambient conditions. We discuss the implications of our discovery, how it can be reconciled with experimental observations and how the ferrielectric phase could be obtained in practice.

Pure PZT95/5 ceramics and its phase transition behavior under external fields

Background: Compositionally modified Pb(Zr0.95Ti0.05)O3 (PZT 95/5) ferroelectric materials are extensively investigated in past decades for many important applications. However, few pure PZT95/5 ceramics were reported. Objective: Herein, pure PZT95/5 ceramics were successfully prepared and their microstructure, phase transition behaviors under external fields were studied. Method: Pure PZT95/5 ceramics were prepared by conventional solid state reaction using a mixed oxide route. The microstructure and its properties under different external fields were measured. Results: The X-ray diffraction patterns indicate that the virgin pure PZT95/5 ceramics exhibit an orthorhombic antiferroelectric phase, also evidenced by the superlattice reflections in SAED pattern. While a rhombohedral ferroelectric symmetry crystal structure was observed in the pooled samples suggesting that an electric field induced antiferroelectric to ferroelectric phase transition occured. Pure PZT95/5 ceramics exhibited a quenched ferroelectric hysteresis loop with a remnant polarization of ~8μC/cm2 under 3.5kV/mm. Temperature dependence dielectric response indicated that orthorhombic antiferroelectric to cubic paraelectric phase transition occured at 225oC, corresponding to its Curie temperature. A shard depolarization behavior and dielectric anomalies were observed under ~240 MPa hydrostatic pressure. Conclusions: The depolarization mechanism of pure PZT95/5 ceramics under hydrostatic pressure is attributed to the hydrostatic pressure induced FE-AFE phase transition. These results will offer fundamental insights into PZT95/5 ceramics for pulsed power supply applications.

Defects and Lattice Instability in Doped Lead-Based Perovskite Antiferroelectrics: Revisited

This paper is a summary of earlier results that have been completed with recent investigations on the nature and sequence of phase transitions evolving in the antiferroelectric PbZrO3 single crystals doped with niobium and Pb(Zr0.70Ti0.30)O3 ceramics doped with different concentration of Bi2O3. It was found that these crystals undergo new phase transitions never observed before. To investigate all phase transitions, different experimental methods were used to characterize the crystal properties. Temperature and time dependencies have been tentatively measured in a wide range, including a region above Tc, where precursor dynamics is observed in the form of non-centrosymmetric regions existing locally in crystal lattices. Also, coexistence of antiferroelectric phase and one of the intermediate phases could be observed in a wide temperature range. The phase transition mechanism in PbZrO3 is discussed, taking into account the local breaking of the crystal symmetry above Tc and the defects of crystal lattices, i.e., those generated during crystal growth, and intentionally introduced by preheating in a vacuum or doping with hetero-valent dopant.

Lead-free (Ag,K)NbO3 materials for high-performance explosive energy conversion

Explosive energy conversion materials with extremely rapid response times have broad and growing applications in energy, medical, defense, and mining areas. Research into the underlying mechanisms and the search for new candidate materials in this field are so limited that environment-unfriendly Pb(Zr,Ti)O3 still dominates after half a century. Here, we report the discovery of a previously undiscovered, lead-free (Ag0.935K0.065)NbO3 material, which possesses a record-high energy storage density of 5.401 J/g, enabling a pulse current ~ 22 A within 1.8 microseconds. It also exhibits excellent temperature stability up to 150°C. Various in situ experimental and theoretical investigations reveal the mechanism underlying this explosive energy conversion can be attributed to a pressure-induced octahedral tilt change from a−a−c+ to a−a−c−/a−a−c+, in accordance with an irreversible pressure-driven ferroelectric-antiferroelectric phase transition. This work provides a high performance alternative to Pb(Zr,Ti)O3 and also guidance for the further development of new materials and devices for explosive energy conversion.

The complex oxides with octahedral structures: Existence areas and phase transitions

The experimental and calculated data on the existence of complex oxides in solid state with the octahedral structures of four families, namely perovskites, Bi-containing layered perovskite-like ones, tetragonal tungsten bronzes and pyrochlores, and about their phase transitions are systematized and summarized on the basis of the quasi-elastic or geometric models of these structures. It has been established that similar existence areas and similar correlations between the interatomic bond strains in their structures, on the one hand, and the temperatures of their ferroelectric or antiferroelectric phase transitions, on the other hand, are observed for all of them, despite the differences in the compositions and structures of these oxides, but taking into account their similar parameters.

Large energy-storage density in transition-metal oxide modified NaNbO3–Bi(Mg0.5Ti0.5)O3 lead-free ceramics through regulating the antiferroelectric phase structure

The combination of AFE phase structural regulation and breakdown strength optimization through chemical modification leads to a large energy-storage density of Wrec ∼ 5.57 J cm−3 in NN–BMT lead-free bulk ceramics.