Local Structure and Order–Disorder Transitions in “Empty” Ferroelectric Tetragonal Tungsten Bronzes

Abstract

The 'empty' tetragonal tungsten bronze Ba 4 La 0.67 ◻ 1.33 Nb 10 O 30 displays both relaxor-like and normal dielectric anomalies as a function of temperature; the former is associated with loss of ferroelectricity and was proposed to originate from anion disordering [Chem. Mater., 2016, 28, 4616-4627]. Here we present total neutron scattering and pair distribution function (PDF) analysis which shows an increase in the distribution of oxygen-oxygen distances at the relaxor transition and which supports the proposed anion disordering mechanism. The disordering process can be destabilized by reducing the average A-cation size (i.e. Nd-doping: Ba 4 (La 1-x Nd x ) 0.67 Nb 10 O 30 ); this introduces a more strongly propagating tilt system in line with the previously reported crystal-chemical framework model [Chem. Mater., 2015, 27, 3250-3261]. Mechanical loss data obtained using resonant ultrasound spectroscopy also indicate destabilisation of the disordering process with increasing Nd-substitution.

Ferroelectric-Relaxor Crossover and Energy Storage Properties in Sr2NaNb5O15-Based Tungsten Bronze Ceramics

“…18−20 Recently, the importance of crystallographic vacancies for additional structural disorders and relaxors was emphasized again. 21,22 However, the modification of relaxor−ferroelectric crossover of SNN under a rich theoretical background is rare, and it is mainly based on B-site cation substitution. 9,19 It must be noted that no clear frequency dispersion was observed, although Zheng et al…”

“…For instance, Ba 4 Sm 2 Zr 4 Nb 6 O 30 is a classical ferroelectric, while Ba 4 La 2 Zr 4 Nb 6 O 30 is a relaxor with a P r value that is nearly zero . The influence mechanisms of B-site cations on the relaxor behavior were also proposed, such as the reduction of the second-order Jahn–Teller distortion (SOJT), which was caused by weak bonding, and the percolation of polar oxygen octahedra in a non-polar matrix. − Recently, the importance of crystallographic vacancies for additional structural disorders and relaxors was emphasized again. , However, the modification of relaxor–ferroelectric crossover of SNN under a rich theoretical background is rare, and it is mainly based on B-site cation substitution. , It must be noted that no clear frequency dispersion was observed, although Zheng et al claimed to obtain a Ca-doped SNN relaxor for energy storage . It is necessary to further explore the potential relaxor behavior regulation mechanism to evaluate the possibility of SNN as an energy storage capacitor, especially the dielectric layer of the BME-MLCC.…”

Role of Incommensurate Modulation in Ba4(Sm1–xLax)2Ti4Nb6O30 Tetragonal Tungsten Bronzes

“…The situation in tungsten bronzes is more complicated and is usually accompanied by various structure modulations. In K 4 R 2 Nb 10 O 30 (R = rare earth), an antiferroelectric-like state was detected between the paraelectric and ferroelectric phases. , The pinched hysteresis loops in the “empty” TTBs Ba 4 (La 1– x Nd x ) 0.67 Nb 10 O 30 were attributed to a local order–disorder transition, while the driving electric field of the transition increased with temperature, indicating increased stability of the disorder with increasing thermal energy. , Pinched loops were also observed in filled TTBs Ba 4 Sm 2 Ti 4 Nb 6 O 30 and Ba 4 Eu 2 Ti 4 Nb 6 O 30 and associated with a field-driven incommensurate-to-commensurate transition, as reported in our previous work . Further investigation reveals the close relationship between the incommensurate (IC)–commensurate (C) and the ferroelectric–paraelectric transition, and the driving electric field of the IC–C transition here decreased when temperature rises close to the ferroelectric–paraelectric transition temperature T C .…”

“…Another feature is the pinched hysteresis loop observed recently in various materials with the perovskite or tungsten bronze structure, and various mechanisms have been investigated and proposed. − The main feature of the pinched P – E hysteresis loop is that the polarization, P r , for a zero electric field is small but finite, unlike ferroelectrics (large P r ) and antiferroelectrics (zero P r ) . Generally, the existence of pinched P – E hysteresis loops is attributed to strong domain wall pinning due to the diffusion of charged defects in some Pb­(Zr,Ti)­O 3 solid solutions − and (Bi 0.5 Na 0.5 )­TiO 3 -based ceramics .…”

Superior Energy Density Achieved in Unfilled Tungsten Bronze Ferroelectrics via Multiscale Regulation Strategy

“…[ 29 , 33 , 34 ] Additionally, the introduction of A‐site vacancies can induce extra changes in the local coordination environment, structure relaxation, and charge/structure disorder. [ 26 , 35 , 36 , 37 ] Consequently, various methods can be adopted to adjust the relaxor behaviors of TTBS ceramics, and their flexible structures and abundant properties tunability provide a suitable realm for the effective design of high energy storage performance. [ 38 ] Hence, the TTBS ceramic family merits more attention and investigation as an energy storage material.…”