Perovskite lead-free dielectrics for energy storage applications

The syntheses, crystal structures, electrical properties, and optical absorbance spectra of six perovskite oxynitrides, AMO2N (A = Ba, Sr, Ca; M = Ta, Nb) have been investigated. The average crystal structure of BaTaO2N is a cubic perovskite, with a Ta−O/N distance of 2.056 A. SrTaO2N and CaTaO2N are distorted by octahedral tilting, showing noticeably smaller Ta−O/N distances of approximately 2.02 A. Electron diffraction studies of BaTaO2N are consistent with the simple cubic perovskite crystal structure determined using X-ray powder diffraction methods. Each of the niobium oxynitrides is isostructural with its tantalum analogue, though the Nb−O/N distances are observed to be slightly longer. The optical band gaps are estimated from diffuse reflectance spectra as follows:  BaTaO2N, 1.8 eV; SrTaO2N, 2.1 eV; CaTaO2N, 2.4 eV; BaNbO2N, 1.8 eV; SrNbO2N, 1.9 eV; CaNbO2N, 2.1 eV. Impedance spectroscopy was carried out on sintered pellets of the ATaO2N and BaNbO2N to investigate the dielectric and electrical tran...

Characterization of the Structural, Optical, and Dielectric Properties of Oxynitride Perovskites AMO2N (A = Ba, Sr, Ca; M = Ta, Nb)

A comprehensive review on the latest development of the antiferroelectric ↔ ferroelectric phase transition is presented. The abrupt volume expansion and sudden development of polarization at the phase transition has been extensively investigated in PbZrO3-based perovskite ceramics. New research developments in these compositions, including the incommensurate domain structure, the auxetic behavior under electric fields in the induced ferroelectric phase, the ferroelastic behavior of the multicell cubic phase, the impact of radial compression, the unexpected electric field-induced ferroelectric-to-antiferroelectric transition, and the phase transition mechanical toughening effect have been summarized. Due to their significance to leadfree piezoelectric ceramics, compounds with antiferroelectric phases, including NaNbO3, AgNbO3, and (Bi1/2Na1/2)TiO3, are also critically reviewed. Focus has been placed on the (Bi1/2Na1/2)TiO3–BaTiO3 solid solution where the electric field-induced ferroelectric phase remains even after the applied field is removed at room temperature. Therefore, the electric field-induced antiferroelectric-to-ferroelectric phase transition is a key to the poling process to develop piezoelectricity in morphotropic phase boundary (MPB) compositions. The competing phase transition and domain switching processes in 0.93 (Bi1/2Na1/2)TiO3–0.07BaTiO3 are directly imaged with nanometer resolution using the unique in situ transmission electron microscopy (TEM) technique.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1189&context=mse_pubs

The Antiferroelectric ↔ Ferroelectric Phase Transition in Lead-Containing and Lead-Free Perovskite Ceramics

The crystal structures of the [A(1)(2)][A(2)(3)](BO(4))(3)X apatites and the related compounds [A(1)(2)][A(2)(3)](BO(5))(3)X and [A(1)(2)][A(2)(3)](BO(3))(3)X are collated and reviewed. The structural aristotype for this family is Mn(5)Si(3) (D8(8) type, P6(3)/mcm symmetry), whose cation array approximates that of all derivatives and from which related structures arise through the systematic insertion of anions into tetrahedral, triangular or linear interstices. The construction of a hierarchy of space-groups leads to three apatite families whose high-symmetry members are P6(3)/m, Cmcm and P6(3)cm. Alternatively, systematic crystallographic changes in apatite solid-solution series may be practically described as deviations from regular anion nets, with particular focus on the O(1)-A(1)-O(2) twist angle phi projected on (001) of the A(1)O(6) metaprism. For apatites that contain the same A cation, it is shown that phi decreases linearly as a function of increasing average ionic radius of the formula unit. Large deviations from this simple relationship may indicate departures from P6(3)/m symmetry or cation ordering. The inclusion of A(1)O(6) metaprisms in structure drawings is useful for comparing apatites and condensed-apatites such as Sr(5)(BO(3))(3)Br. The most common symmetry for the 74 chemically distinct [A(1)(2)][A(2)(3)](BO(4))(3)X apatites that were surveyed was P6(3)/m (57%), with progressively more complex chemistries adopting P6(3) (21%), P3; (9%), P6 (4.3%), P2(1)/m (4.3%) and P2(1) (4.3%). In chemically complex apatites, charge balance is usually maintained through charge-coupled cation substitutions, or through appropriate mixing of monovalent and divalent X anions or X-site vacancies. More rarely, charge compensation is achieved through insertion/removal of oxygen to produce BO(5) square pyramidal units (as in ReO(5)) or BO(3) triangular coordination (as in AsO(3)). Polysomatism arises through the ordered filling of [001] BO(4) tetrahedral strings to generate the apatite-nasonite family of structures.

/pdf/structural-derivation-and-crystal-chemistry-of-apatites-14z08hfu2j.pdf

Structural derivation and crystal chemistry of apatites.

Neutron diffraction studies using powder samples have been used to understand the complex sequence of low temperature phase transitions of $\mathrm{Na}\mathrm{Nb}{\mathrm{O}}_{3}$ in the temperature range from $12\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Detailed Rietveld analysis of the diffraction data reveals that the antiferroelectric to ferroelectric phase transition occurs on cooling around $73\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, while the reverse ferroelectric to antiferroelectric transition occurs on heating at $245\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. However, the former transformation is not complete until it reaches $12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and there is unambiguous evidence for the presence of the ferroelectric $R3c$ phase coexisting with an antiferroelectic phase $(Pbcm)$ over a wide range of temperatures. The coexisting phases and reported anomalous smearing of the dielectric response akin to dipole glasses and relaxors observed in the same temperature range are consistent with competing ferroelectric and antiferroelectric interactions in $\mathrm{Na}\mathrm{Nb}{\mathrm{O}}_{3}$. We have carried out theoretical lattice dynamical calculations which reveal that the free energies of the antiferroelectric $Pbcm$ and ferroelectric $R3c$ phases are nearly identical over a wide range of temperature. The small energy difference between the two phases is of interest as it explains the observed coexistence of these phases over a wide range of temperature. The computed double well depths and energy barriers from paraelectric $Pm\overline{3}m$ to antiferroelectric $Pbcm$ and ferroelectric $R3c$ phases in $\mathrm{Na}\mathrm{Nb}{\mathrm{O}}_{3}$ are also quite similar, although the ferroelectric $R3c$ phase has a slightly lower energy.

https://arxiv.org/pdf/cond-mat/0703365.pdf

K. Łukaszewicz

Papers

The high-temperature phases of sodium niobate and the nature of transitions in pseudosymmetric structures