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Title: High-resolution neutron powder diffraction study on the phase transitions in BaPbO{sub 3}

Abstract

Phase transitions that occurred in perovskite BaPbO{sub 3} have been investigated using high-resolution time-of-flight neutron powder diffraction. The structure at room temperature is orthorhombic (space group Imma), which is derived from the cubic aristotype by tilting the PbO{sub 6} octahedra around the two-fold axis (tilt system a {sup 0} b {sup -} b {sup -}). The orthorhombic structure shows anisotropic line broadening attributed to the presence of micro twins. At above about 573 K, BaPbO{sub 3} undergoes a discontinuous phase transition to a tetragonal structure (space group I4/mcm) with the tilting of the PbO{sub 6} octahedra being about the four-fold axis of the cubic aristotype (tilt system a {sup 0} a {sup 0} c {sup -}). With further increasing the temperature, BaPbO{sub 3} experiences a continuous phase transition to a simple cubic structure (space group Pm3-barm) at above about 673 K. The later phase transition is characterised by a critical exponent of {beta}=0.36, depicted by the three-dimensional Heisenberg universality class. The earlier reported Imma{sup {yields}}I2/m phase transition above room temperature has not been observed. - Graphical abstract: Temperature dependence of the octahedral tilting angles in BaPbO{sub 3}. The continuous line in tetragonal phase region is the fit to the expression:more » {phi}=A(T {sub c}-T) {sup {beta}} with the fitted values of T {sub c}=658(1) K, {beta}=0.36(2) and A=1.1(1). The shaded area indicates the possible two-phase region.« less

Authors:
 [1];  [2];  [3];  [4]
  1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands), E-mail: w.fu@chem.leidenuniv.nl
  2. NWO-Physics, ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom)
  3. ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom)
  4. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands)
Publication Date:
OSTI Identifier:
21015809
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 5; Other Information: DOI: 10.1016/j.jssc.2007.03.009; PII: S0022-4596(07)00106-5; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANISOTROPY; CUBIC LATTICES; LINE BROADENING; NEUTRON DIFFRACTION; ORTHORHOMBIC LATTICES; PEROVSKITE; PHASE TRANSFORMATIONS; SPACE GROUPS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; TEMPERATURE RANGE 0400-1000 K; TETRAGONAL LATTICES; TIME-OF-FLIGHT METHOD

Citation Formats

Fu, W.T., Visser, D., Knight, K.S., and IJdo, D.J.W.. High-resolution neutron powder diffraction study on the phase transitions in BaPbO{sub 3}. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.03.009.
Fu, W.T., Visser, D., Knight, K.S., & IJdo, D.J.W.. High-resolution neutron powder diffraction study on the phase transitions in BaPbO{sub 3}. United States. doi:10.1016/j.jssc.2007.03.009.
Fu, W.T., Visser, D., Knight, K.S., and IJdo, D.J.W.. Tue . "High-resolution neutron powder diffraction study on the phase transitions in BaPbO{sub 3}". United States. doi:10.1016/j.jssc.2007.03.009.
@article{osti_21015809,
title = {High-resolution neutron powder diffraction study on the phase transitions in BaPbO{sub 3}},
author = {Fu, W.T. and Visser, D. and Knight, K.S. and IJdo, D.J.W.},
abstractNote = {Phase transitions that occurred in perovskite BaPbO{sub 3} have been investigated using high-resolution time-of-flight neutron powder diffraction. The structure at room temperature is orthorhombic (space group Imma), which is derived from the cubic aristotype by tilting the PbO{sub 6} octahedra around the two-fold axis (tilt system a {sup 0} b {sup -} b {sup -}). The orthorhombic structure shows anisotropic line broadening attributed to the presence of micro twins. At above about 573 K, BaPbO{sub 3} undergoes a discontinuous phase transition to a tetragonal structure (space group I4/mcm) with the tilting of the PbO{sub 6} octahedra being about the four-fold axis of the cubic aristotype (tilt system a {sup 0} a {sup 0} c {sup -}). With further increasing the temperature, BaPbO{sub 3} experiences a continuous phase transition to a simple cubic structure (space group Pm3-barm) at above about 673 K. The later phase transition is characterised by a critical exponent of {beta}=0.36, depicted by the three-dimensional Heisenberg universality class. The earlier reported Imma{sup {yields}}I2/m phase transition above room temperature has not been observed. - Graphical abstract: Temperature dependence of the octahedral tilting angles in BaPbO{sub 3}. The continuous line in tetragonal phase region is the fit to the expression: {phi}=A(T {sub c}-T) {sup {beta}} with the fitted values of T {sub c}=658(1) K, {beta}=0.36(2) and A=1.1(1). The shaded area indicates the possible two-phase region.},
doi = {10.1016/j.jssc.2007.03.009},
journal = {Journal of Solid State Chemistry},
number = 5,
volume = 180,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Dielectric, piezoelectric resonance frequency, and powder neutron diffraction studies as a function of temperature have been performed on several compositions of (1-x)[Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}]-xPbTiO{sub 3} (PMN-xPT) ceramics in and outside the morphotropic phase boundary (MPB) region to investigate the phase transitions and phase stabilities in this mixed system. Anomalies in the temperature dependence of piezoelectric resonance frequency and dielectric constant are correlated with structural changes using Rietveld analysis of powder neutron diffraction data. The frequency dependent dielectric studies reveal relaxor ferroelectric behavior for x<0.35 and a normal ferroelectric behavior for x{>=}0.35. The dielectric peak temperature and the Vogel-Fulcher freezingmore » temperature are found to increase linearly with 'x' while their difference, after decreasing linearly with x, vanishes at x=0.35 suggesting a crossover form relaxor ferroelectric to normal ferroelectric behavior at this composition. A phase diagram of the PMN-xPT system showing the stability fields of ergodic relaxor, monoclinic M{sub B}, monoclinic M{sub C}, tetragonal and cubic phases is presented. Our results suggest the presence of a succession of three phase transitions, not reported earlier, corresponding to structural changes from the monoclinic M{sub B} to the monoclinic M{sub C} to the tetragonal to the cubic phases for 0.27{<=}x{<=}0.30 on heating above room temperature. In addition, our studies confirm the earlier findings on transitions from the monoclinic M{sub C} to the tetragonal to the cubic phases for 0.31{<=}x{<=}0.34 on heating above room temperature and tetragonal to monoclinic M{sub C} phase on cooling below room temperature for x=0.36. All these transitions are found to be accompanied with anomalies either in the temperature dependence of dielectric constant or the piezoelectric resonance frequency or both. Rietveld analyses of the powder neutron diffraction data at various temperatures on a pseudorhombohedral composition with x=0.25 suggest that the short range M{sub B} type monoclinic order present at room temperature grows to long range monoclinic order on lowering the temperature. The temperature variations of the unit cell parameters and atomic shifts are also presented to throw light on the nature of the various phase transitions in this mixed system.« less
  • The crystal structure and stability of Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065K in p(O{sub 2})=1bar and decomposes according to the eutectoid reaction Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}}+x O{sub 2}-bar Ba{sub 2}CuO{sub 3.4}+CaO+2BaCuO{sub 2}. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, a=8.1452(1)A, {delta}=0.68, Z=2, R{sub wp}=2.5%, R{sub Bragg}=5.4%) asmore » reported in the literature. In reduced oxygen partial pressure (p(O{sub 2})<10{sup -6}bar), Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, a=8.1976(3)A, c=8.0709(3)A, {delta}=-0.81, Z=2, R{sub wp}=2.8%, R{sub Bragg}=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba{sub 4}CaCu{sub 3}O{sub 8+{delta}} is also discussed.« less
  • The phase stabilities of ecofriendly piezoelectric material of lithium doped sodium niobate for composition Li{sub 0.12}Na{sub 0.88}NbO{sub 3} (LNN12) have been investigated by a combination of powder X-ray and neutron diffraction techniques in the temperature range of 300–1100 K. We observed interesting changes with appearance or disappearance of the super-lattice reflections in the powder diffraction patterns. Unambiguous experimental evidence is shown for coexistence of paraelectric and ferroelectric orthorhombic phases in the temperature range of 525 K to 675 K. We identified the correct crystal structure of LNN12 with temperature and correlated it with observed anomaly in the physical properties. Identification of crystal structuremore » also helps in the mode assignments in Raman and infrared spectroscopies. We argued that application of chemical pressure as a result of Li substitution in NaNbO{sub 3} matrix favors the freezing of zone centre phonons in contrast to the freezing of zone boundary phonons in pure NaNbO{sub 3} with the variation of temperature.« less
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  • The structures of (KCN)/sub x/(KBr)/sub 1-x/ mixed crystals for x = 0.95, 0.90, and 0.80 have been determined as a function of temperature. As the temperature is decreased from 295 K, where all of the samples are cubic (as are pure KCN and KBr), all samples measured transform to a monoclinic structure (space group Cc). For x = 0.95 and 0.90, at a lower temperature there is a further transition to an orthorhombic structure similar to that found for pure KCN below 168 K. However, the samples do not transform completely, and the monoclinic and orthorhombic structures coexist down tomore » 6 K. More of the sample transforms for x = 0.95 than for x = 0.90. In both cases, that part of the sample which goes into the orthorhombic phase orders completely at the lowest temperatures, in a structure similar to that found for pure KCN at 6 K.« less