A covalency model of ferroic phase transitions in perovskites

Thomann, H.

doi:10.1080/00150198708227917

Cited by 42 publications

(13 citation statements)

References 9 publications

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“…Above x = 0.3 a third FE phase is induced in these solid solutions. This experimental fact is in agreement with the covalency model of phase transitions by Thomann [32,33]. According to this model the decrease in average electronegativity leads to a transformation from ionic to covalent interactions and accounts for the ferroelectric lattice distortion.…”

Section: Discussionsupporting

confidence: 84%

Phase Transitions in PbZr_1−xSn_xO₃Single Crystals

Jankowska‐Sumara

Dec

2004

Ferroelectrics

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The phase diagram of PbZr 1−x Sn x O 3 (0 ≤ x ≤ 0.4) has been investigated for single crystals by dielectric and optic measurements. The stability of the antiferroelectric Pbam phase was observed for 0 ≤ x ≤ 0.05. Au Sn 4+ content above x > 0.05 induces another antiferroelectric P222 1 phase. At concentrations higher than x = 0.3 a phase of ferroelectric character (R3m) becomes stable. Above x = 0.15 the crossover from sharp to diffuse behaviour of the phase transition takes place. The changes in the phase transitions character and the mechanism leading to the appearance of new anti-and ferroelectric phases are discussed.

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Section: Discussionsupporting

confidence: 84%

Phase Transitions in PbZr_1−xSn_xO₃Single Crystals

Jankowska‐Sumara

Dec

2004

Ferroelectrics

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“…1 b. The increased lattice distortion can be interpreted as a lowering of symmetry, which is believed to be associated with octahedral tilting [ 33 , 34 ]. The need for this octahedral tilting is determined by the volume matching degree between the BO 6 octahedron and the AO 12 polyhedron.…”

Section: Resultsmentioning

confidence: 99%

Practical high-performance lead-free piezoelectrics: structural flexibility beyond utilizing multiphase coexistence

Liu

Zhang

Gao

et al. 2019

National Science Review

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Due to growing concern for the environment and human health, searching for high-performance lead-free piezoceramics has been a hot topic of scientific and industrial research. Despite the significant progress achieved toward enhancing piezoelectricity, further efforts should be devoted to the synergistic improvement of piezoelectricity and its thermal stability. This study provides new insight into these topics. A new KNN-based lead-free ceramic material is presented, which features a large piezoelectric coefficient (d33) exceeding 500 pC/N and a high Curie temperature (Tc) of ∼200°C. The superior piezoelectric response strongly relies on the increased composition-induced structural flexibility due to lattice softening and decreased unit cell distortion. In contrast to piezoelectricity anomalies induced via polymorphic transition, this piezoelectricity enhancement is effective within a broad temperature range rather than a specific small range. In particular, a hierarchical domain architecture composed of nano-sized domains along the submicron domains was detected in this material system, which further contributes to the high piezoelectricity.

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“…The chemistries determining ferroelectricity in each structure requires specific types of mixed ionic and covalent bonding as pointed out early on from Megaw 83 and Thomann. 84 This concept was later refined through first principle calculations by Cohen. 85 He specifically pointed to the case of ferroelectricity in BaTiO 3 and PbTiO 3 , noting that hybridization between an empty Ti 3d orbital and occupied oxygen 2p orbitals reduces the short-range repulsions (which favor the nonpolar cubic structure), permits the off-center displacement of the Ti-ion, and stabilizes the ferroelectric state (with long-range Coulomb forces).…”

Section: Phase Transition Behavior In Ferroelectrics and Their Solid mentioning

confidence: 99%