Evidence of short-range antiferroelectric local states in lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric ceramics

Abstract

Structural and electrical measurements were performed on lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric (FE) ceramics. Dielectric properties show a well-defined relaxor anomaly around −50 °C with double-loop hysteresis curves from this point to the transition temperature. The thesis of short-range antiferroelectric (AFE) local states having incommensurate (INC) structure embedded in the FE polar matrix is proposed to explain the observed behavior. Structural lattice parameters show negative expansion coefficients and INC superlattice diffraction spots were observed through the selected-area diffraction patterns in the [110] zone for this minority local states. The titanium modification of this system seems to be the key fact in the coupling of the INC structure to the AFE local states in the FE–AFE coexistence region.

Relaxor-to-Ferroelectric Crossover and Disruption of Polar Order in “Empty” Tetragonal Tungsten Bronzes

“…72−75 An AFE-FE-PE phase transition sequence was described by Ravez and colleagues in the TTB-like compounds in the solid solution Ba responsible for the weakening of the polar FE ordering, favoring the formation of the AFE state. 73 However, the required crystallographic antipolar arrangement for antiferroelectricity is not evident in the compositions studied here, and so, long-range AFE order can be discounted. Other mechanisms shown to affect such P−E behavior include: double loops within a narrow temperature range close to T C due to an electric field driven transition between the paraelectric and ferroelectric phases in ferroelectrics with a sharp first order ferroelectric-paraelectric phase transition (e.g., undoped BaTiO 3 ) 54 and defect dipoles in aged ferroelectrics.…”

“…Such loops, first demonstrated in PbZrO 3 by Shirane et al, , are characteristic of AFE ordering, and consequently, many systems were designated as being AFE based on P – E loops. Few instances of pinched “antiferroelectric” loops have been reported in TTBs. − An AFE-FE-PE phase transition sequence was described by Ravez and colleagues in the TTB-like compounds in the solid solution Ba 2.14 Li 0.71 Nb 5 O 15 –Ba 2.14 Li 0.71 Ta 5 O 15 (i.e., Ba 4.28 Li 1.42 Nb 10 O 30 –Ba 4.28 Li 1.42 Ta 10 O 30 ). , Gagou et al have recently attributed two dielectric anomalies in K 4 Gd 2 Nb 10 O 30 to a FE-AFE-PE sequence of phase transitions based on Raman spectroscopy data; however, no P – E loops were demonstrated, and the low temperature anomaly has previously been associated with a ferroelastic related transition between orthorhombic (pseudotetragonal) and tetragonal structures . Pinched P – E loops have been reported in La and Ti codoped SBN, Sr 0.255 Ba 0.7 La 0.03 Nb 2‑ y Ti y O 6‑δ with y = 0.05 (i.e., Sr 1.275 Ba 3.5 La 0.15 Nb 9.75 Ti 0.25 O 30‑δ ) in which FE and AFE states coexist.…”

“…500 K. 73 However, the required crystallographic anti-polar arrangement for antiferroelectricity is not evident in the compositions studied here and so long range AFE order can be discounted.…”

“…Pinched P−E loops have been reported in La and Ti codoped SBN, Sr 0.255 Ba 0.7 La 0.03 Nb 2-y Ti y O 6-δ with y = 0.05 (i.e., Sr 1.275 Ba 3.5 La 0.15 Nb 9.75 Ti 0.25 O 30-δ ) in which FE and AFE states coexist. The authors suggest a polar FE matrix with commensurate tetragonal structure within which local ordering of an incommensurately modulated AFE structure occurs 73. Ti 4+ dopant-induced defects were suggested as being…”

Ferroelectric to relaxor crossover in Li solid solutions derived from Ba2Nd□2FeNb4O15

“…These contradictory observations, however, are mitigated by the fact that the aforementioned off-centering is an in-plane displacement. Since a 4fold axis lies along the c axis, a displacement in the ab plane of B2 cation must result in an antiparallel arrangement of dipoles, which should be associated with an antiferroelectric behaviour obviously [30,36]. Since a ferroelectric behaviour is observed for x up to 0.18 while the off-centering is maximized for x=0,24, the dielectric signature in this system may be the result of competing ferroelectric and antiferroelectric states related to a subtle distortion mechanism.…”