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Frantti J.,Finnish Research and Engineering | Fujioka Y.,Finnish Research and Engineering | Zhang J.,Los Alamos National Laboratory | Zhu J.,Los Alamos National Laboratory | And 2 more authors.
Review of Scientific Instruments | Year: 2014

Piezoelectric materials respond to external stimuli by adjusting atomic positions. In solid-solutions, the changes occurring in atomic scale are very complex since the short- and long-range order are different. Standard methods used in diffraction data analysis fail to model the short-range order accurately. Pressure-induced cation displacements in ferroelectric Pb(Zr 0.45Ti0.55)O3 perovskite oxide are modeled by starting from a short-range order. We show that the model gives the average structure correctly and properly describes the local structure. The origin of the microstrain in lead zirconate titanate is the spatially varying Zr and Ti concentration and atomic distances, which is taken into account in the simulation. High-pressure neutron powder diffraction and simulation techniques are applied for the determination of atomic positions and bond-valences as a function of pressure. Under hydrostatic pressure, the material loses its piezoelectric properties far before the transition to the cubic phase takes place. The total cation valence +6 is preserved up to 3.31 GPa by compensating the increasing B-cation valence by decreasing Pb-displacement from the high-symmetry position. At 3.31 GPa, Pb-displacement is zero and the material is no more ferroelectric. This is also the pressure at which the Pb-valence is minimized. The average structure is still tetragonal. The model for microstrain predicts that the transition occurs over a finite pressure range: Pb-displacements are spatially varying and follow the distribution of Zr and Ti ions. © 2014 AIP Publishing LLC. Source

Frantti J.,Finnish Research and Engineering | Fujioka Y.,Finnish Research and Engineering | Puretzky A.,Oak Ridge National Laboratory | Xie Y.,Simon Fraser University | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2015

A single crystal of lead-zirconate-titanate, composition Pb(Zr0.80Ti0.20)O3, was studied by polarized-Raman scattering as a function of temperature. Raman spectra reveal that the local structure deviates from the average structure in both ferroelectric and paraelectric phases. We show that the crystal possesses several, inequivalent complex domain boundaries which show no sign of instability even 200 K above the ferroelectric-to-paraelectric phase transition temperature TC. Two types of boundaries are addressed. The first boundary was formed between ferroelectric domains below TC. This boundary remained stable up to the highest measurement temperatures, and stabilized the domains so that they had the same orientation after repeated heating and cooling cycles. These domains transformed normally to the cubic paraelectric phase. Another type of boundary was formed at 673 K and exhibited no signs of instability up to 923 K. The boundary formation was reversible: it formed and vanished between 573 and 673 K during heating and cooling, respectively. A model in which the crystal is divided into thin slices with different Zr/Ti ratios is proposed. The physical mechanism behind the thermal-stress-induced structural changes is related to the different thermal expansion of the slices, which forces the domain to grow similarly after each heating and cooling cycle. The results are interesting for non-volatile memory development, as it implies that the original ferroelectric state can be restored after the material has been transformed to the paraelectric phase. It also suggests that a low-symmetry structure, stable up to high temperatures, can be prepared through controlled deposition of layers with desired compositions. © 2015 IOP Publishing Ltd. Source

Frantti J.,Finnish Research and Engineering | Fujioka Y.,Finnish Research and Engineering
Materials Today: Proceedings | Year: 2016

A numerical method for solids possessing several defects is applied for modeling x-ray scattering during domain reversal in nanosize lead-zirconate-titanate [Pb(ZrxTi1-x)O3, PZT] clusters. The method models particle size, shape, and defects and isolates element-specific signals. X-ray scattering intensities are computed to show how experimental and computational techniques can be applied for in-situ studies of domain reversal. Two domain boundary types are considered, the first fulfilling the electrical and mechanical compatibility conditions, and the second violating the conditions. During the initial states of the polarization reversal compatibility conditions are violated, which motivated the development of structural models and analysis methods. © 2016 Elsevier Ltd. Source

Frantti J.,Finnish Research and Engineering | Fujioka Y.,Finnish Research and Engineering | Zhang J.,Los Alamos National Laboratory | Zhu J.,Los Alamos National Laboratory | Vogel S.C.,Los Alamos National Laboratory
Physica Status Solidi (B) Basic Research | Year: 2015

This study presents the structural and magnetic properties of solid solutions Pb[Zrx(Fe2/3W1/3)1-x]O3 (PZFW), with x=0.35 and 0.60. The focus is on the study of magnetic ordering and the co-existing electrical dipole moments as a function of temperature. Neutron powder diffraction (NPD) measurements showed that both samples possess a pseudo-cubic structure. A G-type antiferromagnetic (AFM) order onsets at around 150K in PZFW with x=0.35, accompanied by a broad hump in the magnetization, magnetic peak width determined from the NPD patterns, and thermal expansion versus temperature curve, which indicate a diffusive phase transition. Weak anomalous thermal expansion was assigned to the spontaneous magnetostriction. A susceptibility cusp characteristic to an AFM ordering was observed at 15K though no evident change was observed in the NPD patterns at 12K. The magnetic behavior is assigned to different size clusters: with decreasing temperature a larger fraction of the material becomes magnetically ordered. Remnant magnetization was observed in PZFW with x=0.35 at 2K. No magnetic reflections were seen in PZFW with x=0.60 down to 12K. Magnetometer measurements revealed a weak AFM cusp at 8K, confirmed by hysteresis loop measurements. The off-center Pb-displacements and the oxygen octahedra displacement along the cubic axis with respect to the B-cations generate an electric dipole moment. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Fujioka Y.,Finnish Research and Engineering | Frantti J.,Finnish Research and Engineering | Llobet A.,Los Alamos National Laboratory | King G.,Los Alamos National Laboratory | Ehrlich S.N.,Brookhaven National Laboratory
Materials Today: Proceedings | Year: 2016

NiTiO3 and CoTiO3 ilmenites (space group ) form a homogeneous mixture with remarkably low crystal symmetry. According to neutron and synchrotron X-ray powder diffraction measurements, the room-temperature space group symmetry of the Ni0.6Co0.4TiO3 sample is triclinic This structural distortion is the first known case in ilmenites and opens up ways to modify functional properties of magnetic oxides. The origin of the distortion is discussed. Transitions from a paramagnetic to a weak ferromagnetic and further to a ferrimagnetic phase occur at 69 and 25 K, respectively. The ferromagnetic phase is characteristic of the solid-solution and is not found in the constituents. © 2016 Elsevier Ltd. Source

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