Out-of-centre distortions around an octahedrally coordinated Ti4+ in BaTiO3

Gaudon, Manuel

doi:10.1016/j.poly.2014.12.004

Cited by 12 publications

(8 citation statements)

References 25 publications

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“…Similarly, the analysis of the data for BTS10 and BTS12 identified that the samples contain the rhombohedral R3m and cubic Pm3m phases. The rhombohedral phase was not detected by X-ray diffraction measurements in the previous studies (Veselinović et al, 2014;Varez et al, 2004;Gaudon, 2015). This is not surprising as the intensity of the rhombohedral phase reflections strongly depends on the oxygen positions, which, as discussed above, have not been identified mainly because of the insensitivity of X-ray scattering to subtle displacements of O and M atoms along {111} c with respect to Ba (Stokes et al, 2002).…”

Section: Phase-composition-dependent Structural Properties Of the Btsmentioning

confidence: 80%

New insights into BaTi_1–xSn_xO₃ (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

et al. 2016

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Neutron powder diffraction (NPD) was employed to further investigate the BaTi1−xSnxO3 (BTS) system previously studied by X‐ray diffraction. The room‐temperature phase compositions and crystal structures of BTS samples with x = 0, 0.025, 0.05, 0.07, 0.10, 0.12, 0.15 and 0.20 were refined by the Rietveld method using NPD data. It is well known that barium titanate powder (x = 0) crystallizes in the tetragonal P4mm space group. The crystal structures of the samples with 0.025 ≤ x ≤ 0.07 were refined as mixtures of P4mm and Amm2 phases; those with x = 0.1 and 0.12 show the coexistence of rhombohedral R3m and cubic phases, while the samples with x = 0.15 and 0.20 crystallize in a single cubic phase. Temperature‐dependent NPD was used to characterize the BaTi0.95Sn0.05O3 sample at 273, 333 and 373 K, and it was found to form single‐phase Amm2, P4mm and structures at these respective temperatures. The NPD results are in agreement with data obtained by differential scanning calorimetry and dielectric permittivity measurements, which show a paraelectric–ferroelectric transition (associated with structural transition) from to P4mm at about 353 K followed by a P4mm to Amm2 phase transition at about 303 K.

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Section: Phase-composition-dependent Structural Properties Of the Btsmentioning

confidence: 80%

New insights into BaTi_1–xSn_xO₃ (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

et al. 2016

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“…For BaTiO 3 , basic models provide an out-of-center distortion of the octahedral Ti 4+ cations on the B site within a cubic perovskite cell to cause an obvious δ+/δ− linear dipole along a Ti–O bond and a plausible explanation for the shift to a tetragonal unit cell. , More advanced models combine double-well potentials with valence bond theory in order to optimize the effects of short-range ionic attractions and long-range ordering, to arrive at an adiabatic potential energy surface (APES) to describe phase transition sequences. , A more complete picture can be obtained through the application of molecular orbital theory, using the pseudo-Jahn–Teller effect (PJTE) to derive the APES. PJTE theory, developed for perovskites by Bersuker, , combines ground and excited states in vibronic coupling interactions to demonstrate nature’s tendency to avoid degeneracy and pseudodegeneracy by symmetry breaking.…”

Section: Introductionmentioning

confidence: 99%

Stoichiometric Control over Ferroic Behavior in Ba(Ti_1–xFe_x)O₃ Nanocrystals

et al. 2019

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Ba(Ti,Fe)O 3 is a useful system for the exploration of multiferroic properties as a function of composition and variation in structure, based upon a model of intersubstitution of the B site cation. Nanocrystals of Ba(Ti,Fe)O 3 could be used as building blocks for composite multiferroic materials, provided ferroic properties are recognizable at this length scale and Ti and Fe serve as ideal models for the case of d 0 versus d n in a ferroic perovskite. A series of iron-substituted barium titanate nanocrystals (BaTi 1−x Fe x O 3 ) were synthesized at 60 °C using a hybrid sol−gel chemical solution processing method. No further crystallization/ calcination steps were required. The as-prepared nanocrystals are fully crystalline, uniform in size (∼8 nm by TEM), and dispersible in polar organic solvents, yielding nanocrystal/alcohol formulations. Complete consumption of the reactant precursors ensures adequate control over stoichiometry of the final product, over a full range of x (0, 0.1 to 0.75, 1.0). Pair distribution function (PDF) analysis enabled in-depth structural characterization (phase, space group, unit cell parameters, etc.) and shows that, in the case of x = 0, 0.1, 0.2, 0.3, BaTiO 3 , and BaTi 1−x Fe x O 3 nanocrystals, it is concluded that they are tetragonal noncentrosymmetric P4mm with lattice parameters increasing from, e.g., c = 4.04 to 4.08 Å. XPS analysis confirms the presence of both Fe 3+ (d 5 ) and Fe 4+ (d 4 ), both candidates for multiferroicity in this system, given certain spin configurations in octahedral field splitting. The PDF cacluated lattice expansion is attributed to Fe 3+ (d 5 , HS) incorporation. The evidence of noncentrosymmetry, lattice expansion, and XPS conformation of Fe 3+ provides support for the existence of multiferroicity in these sub-10 nm uniform dispersed nanocrystals. For x > 0.5, Fe impacts the structure but still produces dispersible, relatively monodisperse nanocrystals. XPS also shows an increasing amount of Fe 4+ with increasing Fe, suggesting that Fe(IV) is evolving as charge compensation with decreasing Ti 4+ , while attempting to preserve the perovskite structure. A mixture of Fe 3+ /Fe 4+ is thought to reside at the B site: Fe 4+ helps stabilize the structure through charge balancing, while Fe 3+ may be complimented with oxygen vacancies to some extent, especially at the surface. The structure may therefore be of the form BaTi 1−x Fe x O 3-δ for increasing x. At higher concentrations (Fe > 0.5) the emergence of BaFeO 3 and/or BaFe 2 O 4 is offered as an explanation for competing phases, with BaFeO 3 as the likeliest competing phase for x = 1.0. Because of the good dispersibility of the nanocrystals in solvents, spin coating of uniform 0−3 nanocomposite BaTi 1−x Fe x O 3 /polyvinylpyrrolidone thin film capacitors (<0.5 μm) was possible. Frequency dependent dielectric measurements showed stable dielectric constants at 1 MHz of 27.0 to 22.2 for BaTi 1−x Fe x O 3 samples for x = 0−0.75, respectively. Loss tangent

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“…Depending on the temperature, BaTiO 3 has four polymorph phases (cubic, tetragonal, orthorhombic and rhombohedral, consecutively). However, at room temperature, it is tetragonal in structure [ 23 ]. The ferroelectric phase is formed when the temperature decreases, through several phase transitions: cubic (centrosymmetric phase) to tetragonal, orthorhombic and rhombohedral phases.…”

Section: Introductionmentioning

confidence: 99%

Laser Processed Hybrid Lead-Free Thin Films for SAW Sensors

et al. 2022

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In this study we report the specific interaction of various gases on the modified surface of acoustic wave devices for gas sensor applications, using the piezoelectric ceramic material BaSrTiO3 (BST), with different concentrations of Sr. For enhancing the sensitivity of the sensor, the conductive polymer polyethylenimine (PEI) was deposited on top of BST thin films. Thin films of BST were deposited by pulsed laser deposition (PLD) technique and integrated into a test heterostructure with PEI thin films deposited by matrix assisted pulsed laser evaporation (MAPLE) and interdigital Au electrodes (IDT). Further on, the layered heterostructures were incorporated into surface acoustic wave (SAW) devices, in order to measure the frequency response to various gases (N2, CO2 and O2). The frequency responses of the sensors based on thin films of the piezoelectric material deposited at different pressures were compared with layered structures of PEI/BST, in order to observe differences in the frequency shifts between sensors. The SAW tests performed at room temperature revealed different results based on deposition condition (pressure of oxygen and the percent of strontium in BatiO3 structure). Frequency shift responses were obtained for all the tested sensors in the case of a concentration of Sr x = 0.75, for all the analysed gases. The best frequency shifts among all sensors studied was obtained in the case of BST50 polymer sensor for CO2 detection.

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Out-of-centre distortions around an octahedrally coordinated Ti4+ in BaTiO3

Cited by 12 publications

References 25 publications

New insights into BaTi_1–xSn_xO₃ (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

New insights into BaTi_1–xSn_xO₃ (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

Stoichiometric Control over Ferroic Behavior in Ba(Ti_1–xFe_x)O₃ Nanocrystals

Laser Processed Hybrid Lead-Free Thin Films for SAW Sensors

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Out-of-centre distortions around an octahedrally coordinated Ti4+ in BaTiO3

Cited by 12 publications

References 25 publications

New insights into BaTi1–x Sn x O3 (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

New insights into BaTi1–x Sn x O3 (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

Stoichiometric Control over Ferroic Behavior in Ba(Ti1–xFex)O3 Nanocrystals

Laser Processed Hybrid Lead-Free Thin Films for SAW Sensors

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New insights into BaTi_1–xSn_xO₃ (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

New insights into BaTi_1–xSn_xO₃ (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

Stoichiometric Control over Ferroic Behavior in Ba(Ti_1–xFe_x)O₃ Nanocrystals