Flexible relaxor materials: Ba2PrxNd1−xFeNb4O15tetragonal tungsten bronze solid solution

Journal of Physics: Condensed Matter, 2009

Relaxors are very interesting materials but they are most of the time restricted to perovskite materials and thus their flexibility is limited. We have previously shown that tetragonal tungsten bronze (TTB) niobates Ba 2 PrFeNb 4 O 15 was a relaxor below 170K and that Ba 2 NdFeNb 4 O 15 displays a ferroelectric behavior with a T C =323K. On scanning the whole solid solution Ba 2 Pr x Nd 1-x FeNb 4 O 15 (

Journal of Applied Crystallography, 2000

Journal of Thermal Analysis and Calorimetry, 2015

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 was 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 VF 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 instrumentation limits has a dramatic influence on the values obtained.

Relaxor ferroelectricity is one of the most widely investigated but the least understood material classes in the condensed matter physics. This is largely due to the lack of experimental tools that decisively confirm the existing theoretical models. In spite of the diversity in the models, they share the core idea that the observed features in relaxors are closely related to localized chemical heterogeneity. Given this, this review attempts to overview the existing models of importance chronologically, from the diffuse phase transition model to the random-field model and to show how the core idea has been reflected in them to better shape our insight into the nature of relaxor-related phenomena. Then, the discussion will be directed to how the models of a common consensus, developed with the so-called canonical relaxors such as Pb(Mg 1/3 Nb 2/3)O3 (PMN) and (Pb, La)(Zr, Ti)O3 (PLZT), are compatible with phenomenological explanations for the recently identified re-laxors such as (Bi 1/2 Na 1/2)TiO3 (BNT)-based lead-free ferroelectrics. This review will be finalized with a discussion on the theoretical aspects of recently introduced 0−3 and 2−2 ferroelectric/relaxor composites as a practical tool for strain engineering.

Journal of Thermal Analysis and Calorimetry, 2016

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 Ba6GaNb9O30 (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 ...

Chemistry of Materials, 2015

Tetragonal Tungsten Bronzes (TTBs)-an important class of oxides known to exhibit ferroelectricity-undergo complex distortions, including rotations of oxygen octahedra, which give rise to either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dielectric behaviour rather than sharper frequency-independent normal ferroelectric anomalies but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate displacive modulations on the onset of relaxor/ferroelectric behaviour in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition-structure-properties relations for a broad range of TTB systems.

Physical Review Letters, 2009

Despite intensive studies on PbðMg 1=3 Nb 2=3 ÞO 3 (PMN) relaxor, understanding the exact nature of its giant dielectric response and of its physical ground state is a fundamental issue that has remained unresolved for decades. Here, we report a comprehensive study of PMN relaxor crystal, and show that (i) its anomalous dielectric behavior in a broad temperature range results from the reorientation of polarization in the crystal, and (ii) the PMN relaxor is essentially a nanosized ferroelectric material with multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry. Such inhomogeneities are believed to play a crucial role in producing the huge and enigmatic physical effects in relaxor system, and may be used to design other new systems with giant effects such as a relaxor system.

Materials Letters, 2001

w x Ž. Polycrystalline samples of Ba EuTi Zr Nb O x s 0, 1, 2, 3 of Tungsten-Bronze TB structural family have been 5 3 yx x 7 30 Ž. prepared by a high-temperature solid-state reaction technique. X-ray diffraction XRD analysis as a function of temperature shows the orthorhombic structure of the compounds at room temperature. Dielectric studies at four different frequencies, 1, 10, 100 kHz and 1 MHz, show that the above compounds have ferroelectric phase transition of diffuse-type, and also have Ž. relaxor properties. With increasing Zr concentration x , the transition temperature of the compounds decreases.

Materials Research Bulletin, 2013

Journal of Alloys and Compounds

The present work reports the elaboration and physical investigation of new compounds of the following composition Ba 1−x Na x (Ti 1−y Sn y ) 1−x Nb x O 3 (BTSnNxy). The studied ternary system presents some continuous solid solutions between the next 3 phases: the NaNbO 3 antiferroelectric phase that becomes easily ferroelectric at low rate substitutions, the BaTiO 3 ferroelectric phase and the paraelectric stannate phase BaSnO 3 . Two different dielectric behaviors can be observed once some substitutions are made either in A or B sites of an ABO 3 perovskite. These substitutions modify the dielectric properties of the material. The introduction of Sn 4+ and Ti 4+ cations in the B site favors, respectively, a decrease of the transition temperature and an increase in the value of the real dielectric permittivity. The transition temperature should be modulated by varying the rate of cationic substitution. Some relaxor materials can be obtained at a temperature around room temperature.