Ferroelectricity measurements on SrxBa1-xNb2O6

Phil. Trans. R. Soc. A.

Miller

Arnold

et al. 2014

We discuss the strategy for development of novel functional materials with the tetragonal tungsten bronze structure. From the starting composition Ba 6 GaNb 9 O 30 , the effect of A- and B-site substitutions on the dielectric properties is used to develop an understanding of the origin and stability of the dipolar response in these compounds. Both tetragonal strain induced by large B-site cations and local strain variations created by isovalent A-site substitutions enhance dipole stability but result in a dilute, weakly correlated dipolar response and canonical relaxor behaviour. Decreasing cation size at the perovskite A2-site increases the dipolar displacements in the surrounding octahedra, but insufficiently to result in dipole ordering. Mechanisms introducing small A-site lanthanide cations and incorporation of A-site vacancies to induce ferroelectricity and magnetism are presented.

Section: Introductionmentioning

confidence: 99%

Towards novel multiferroic and magnetoelectric materials: dipole stability in tetragonal tungsten bronzes

Phil. Trans. R. Soc. A.

Miller

Arnold

et al. 2014

“…These materials, known to exhibit diverse properties as a result of compositional flexibility and by a higher probability for cation ordering, may offer better ways of attaining room-temperature ferroelectricity and (anti)ferromagnetism, multiferroic behaviour and eventually magnetoelectric coupling [2,8]. Whilst ferroelectric TTBs (including Ba 2 NaNb 5 O 15 [9][10][11] and (Ba,Sr)Nb 2 O 6 [12][13][14]) were widely investigated during the 1960s and 1970s, our understanding of manipulating this structure type is still poor, with the research surprisingly limited compared to that in perovskites [5]. Early attempts focused on tungsten bronzes of nominal composition A 6 B 10 O 30 (mainly compositions where the C-sites are vacant).…”

Section: Introductionmentioning

confidence: 99%

Elastic and anelastic relaxations accompanying relaxor ferroelectric behaviour of Ba6GaNb9O30 tetragonal tungsten bronze from resonant ultrasound spectroscopy

Schiemer

Carpenter

2016

J Therm Anal Calorim

Tetragonal tungsten bronze (TTB) structures offer some promise as lead-free ferroelectrics and have an advantage of great flexibility in terms of accessible composition ranges due to the number of crystallographic sites available for chemical substitution. The ferroic properties of interest are coupled with strain, which will be important in the context of stability, switching dynamics and thin film properties. Coupling of strain with the ferroelectric order parameter gives rise to changes in elastic properties, and these have been investigated for a ceramic sample of Ba 6 GaNb 9 O 30 (BGNO) by resonant ultrasound spectroscopy. Room temperature values of the shear and bulk moduli for BGNO are rather higher than for TTBs with related composition which are orthorhombic at room temperature, consistent with suppression of the ferroelectric transition. Instead, a broad, rounded minimum in the shear modulus measured at *1 MHz is accompanied by a broad rounded maximum in acoustic loss near 115 K and signifies relaxor freezing behaviour. Elastic softening with falling temperature from room temperature, ahead of the freezing interval, is attributed to the development of dynamical polar nanoregions (PNRs), whilst the nonlinear stiffening below *115 K is consistent with a spectrum of relaxation times for freezing of the PNR microstructure.

“…Although several studies attempted to incorporate cations with uncompensated spins into the structure for inducing magnetic ordering, the findings were contradictory and in some cases even incomplete. Whilst ferroelectric TTBs (including Ba 2 NaNb 5 O 15 [24][25][26] and (Ba,Sr)Nb 2 O 6 [27][28][29]) were widely investigated during those years, the amount of study is surprisingly limited relatively to perovskites and our understanding of manipulating this structure type is still poor. In the latest years, there has been a resurgence in research dedicated to discovery of novel TTB ferroelectric and ferroelectric-related (i.e.…”

Section: Introductionmentioning

confidence: 99%

Vogel–Fulcher analysis of relaxor dielectrics with the tetragonal tungsten bronze structure: Ba6MNb9O30 (M = Ga, Sc, In)

Morrison

2015

J Therm Anal Calorim

In-depth analysis of the relaxor behaviour of Ba 6 MNb 9 O 30 (M= Ga, Sc, In) tetragonal tungsten bronze (TTB) ceramics was carried out. Powder x-ray diffraction and scanning electron microscopy were performed in order to confirm the formation of desired phases and to determine the microstructure. Low-temperature dielectric spectroscopy was used in order to characterise the dielectric properties of these materials; the degree of relaxor behaviour were investigated in relation with the increase of ionic radius of the M-cation on the B-site of the TTB structure. The dynamics of dielectric relaxation of dipoles was studied by fitting the dielectric permittivity data to the Vogel-Fulcher (VF) model in order to monitor the reproducibility and validity of the physical results. Restrictions to the VF fit were attempted besides the regular "free-fit" by constraining some of the fundamental relaxation parameters to physically sensible values. We show that Vogel-Fulcher fits are very sensitive to the fitting range resulting in a large range of fundamental parameters for the dielectric relaxation processes, and that the restriction of the frequency domain due to experimental noise or to instrumentation limits has a dramatic influence on the values obtained.