scholarly journals Origin of Structural Change Driven by A-Site Lanthanide Doping in ABO3-Type Perovskite Ferroelectrics

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 434
Author(s):  
Lan Xu ◽  
Zujian Wang ◽  
Bin Su ◽  
Chenxi Wang ◽  
Xiaoming Yang ◽  
...  
Keyword(s):  
Structural Change ◽  
Curie Temperature ◽  
Ferroelectric Materials ◽  
Ferroelectric Crystal ◽  
Internal Factors ◽  
Covalent Bonds ◽  
Lanthanide Doping ◽  
Dramatic Decline ◽  
Change Temperature ◽  
A Site

Lanthanide doping is widely employed to tune structural change temperature and electrical properties in ABO3-type perovskite ferroelectric materials. However, the reason that A-site lanthanide doping leads to the decrease of the Curie temperature is still not clear. Based on the reported Curie temperature of lanthanides (Ln) doped in two classic ferroelectrics PbTiO3 and BaTiO3 with A2+B4+O3-type perovskite structure, we discussed the relationship between the decrease rate of Curie temperature (ΔTC) and the bond strength variance of A-site cation (σ). For Nd ion doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Nd-PMNT) ferroelectric crystal as an example, the internal factors of the dramatic decline of the Curie temperature induced by A-site Nd doping were investigated under a systematic study. The strong covalent bonds of Ln-O play an important role in A-site Ln composition-induced structural change from ferroelectric to paraelectric phase, and it is responsible for the significant decrease in the Curie temperature. It is proposed that the cells become cubic around the Ln ions due to the strong covalent energy of Ln-O bonding in A-site Ln doped A2+B4+O3 perovskite ferroelectrics.

First-principles study of BiFeO3 and BaTiO3 in tetragonal structure

2019 ◽  
Vol 33 (21) ◽  
pp. 1950231
Author(s):  
Akbar Ali ◽  
Imad Khan ◽  
Zahid Ali ◽  
Fawad Khan ◽  
Iftikhar Ahmad
Keyword(s):  
Density Functional ◽  
Coupling Effect ◽  
Ferroelectric Materials ◽  
Bandgap Energy ◽  
Spin Orbit Coupling ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Total Energies ◽  
A Site

Structural, electronic, magnetic and mechanical properties of the perovskites BiFeO3 (BFO) and BaTiO3 (BTO) are investigated using density functional theory (DFT). Structural and mechanical parameters are calculated using generalized gradient approximation (GGA) and the results consistent with the available literature. The stable magnetic phases are achieved by optimizing total energies versus volumes of the cells in different magnetic configurations such as nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM). BTO is found to be NM while BFO favors G-type AFM (G-AFM) phase. The electronic properties are investigated using GGA, GGA with Hubbard potential (GGA[Formula: see text]+[Formula: see text]U) and modified Becke–Johnson (GGA-mBJ) exchange–correlation functionals. BFO is found to be a direct bandgap semiconductor having gap energy value 3.0 eV whereas BTO is an indirect semiconductor with bandgap energy 2.9 eV. Spin–orbit coupling effect is dominant in BFO due to the larger size of A-site cation. The electrical polarization shows that both the compounds are ferroelectric materials with significant spontaneous polarization of 144.1 [Formula: see text]C/cm2 and 27.9 [Formula: see text]C/cm2 for BFO and BTO respectively.

Phase-Dield Simulation of Rhombohedral and Tetragonal Phases in Ferroelectric Single Crystals

Aerospace ◽  
2006 ◽  
Author(s):  
T. Liu ◽  
C. S. Lynch
Keyword(s):  
Free Energy ◽  
Phase Transformations ◽  
Single Crystals ◽  
Electric Fields ◽  
Tetragonal Phase ◽  
Ferroelectric Materials ◽  
Integration Scheme ◽  
Ferroelectric Crystal ◽  
Domain Structures ◽  
Tdgl Equation

Ferroelectric materials exhibit spontaneous polarization and domain structures below the Curie temperature. In this work the phase field approach has been used to simulate phase transformations and the formation of ferroelectric domain structures. The evolution of phases and domain structures was simulated in ferroelectric single crystals by solving the time dependent Ginzburg-Landau (TDGL) equation with polarization as the order parameter. In the TDGL equation the free energy of a ferroelectric crystal is written as a function of polarization and applied fields. Change of temperature as well as application of stress and electric fields leads to change of the free energy and evolution of phase states and domain structures. In this work the finite difference method was implemented for the spatial description of the polarization and the temporal evolution of polarization field was computed by solving the TDGL equation with an explicit time integration scheme. Cubic to tetragonal, cubic to rhombohedral and rhombohedral to tetragonal phase transformations were modeled, and the formation of domain structures was simulated. Field induced polarization switching and rhombohedral to tetragonal phase transition were simulated.

Piezoelectric Properties and Dielectric Property of Li Added KNN Ceramics

2013 ◽  
Vol 566 ◽  
pp. 72-75 ◽  
Author(s):  
Akihiro Mitani ◽  
Yoshinari Oba
Keyword(s):  
Dielectric Property ◽  
Curie Temperature ◽  
Perovskite Structure ◽  
High Performance ◽  
Piezoelectric Properties ◽  
Piezoelectric Materials ◽  
Environmental Issues ◽  
Lead Free ◽  
High Curie Temperature ◽  
A Site

Recently, high performance lead-free piezoelectric materials are strongly demanded for environmental issues. (K0.5Na0.5)NbO3 (KNN) has been attracting interest as lead-free piezoelectric ceramics because of its high Curie temperature and excellent piezoelectric properties. In this study, we investigated effects of Li addition on piezoelectric properties of (Li,Na,K)(Nb+Ta)O3+CuO,BaTiO3 . We found that optimum Li ratio of A site and B site on the perovskite structure increases relative density and .

scholarly journals Vegetation structural change since 1981 significantly enhanced the terrestrial carbon sink

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Jing M. Chen ◽  
Weimin Ju ◽  
Philippe Ciais ◽  
Nicolas Viovy ◽  
Ronggao Liu ◽  
...  
Keyword(s):  
Structural Change ◽  
Carbon Cycle ◽  
Carbon Sink ◽  
Prognostic Models ◽  
Terrestrial Carbon ◽  
Area Index ◽  
Change Temperature ◽  
Temperature Radiation ◽  
Terrestrial Carbon Sink ◽  
The Impact

Abstract Satellite observations show that leaf area index (LAI) has increased globally since 1981, but the impact of this vegetation structural change on the global terrestrial carbon cycle has not been systematically evaluated. Through process-based diagnostic ecosystem modeling, we find that the increase in LAI alone was responsible for 12.4% of the accumulated terrestrial carbon sink (95 ± 5 Pg C) from 1981 to 2016, whereas other drivers of CO2 fertilization, nitrogen deposition, and climate change (temperature, radiation, and precipitation) contributed to 47.0%, 1.1%, and −28.6% of the sink, respectively. The legacy effects of past changes in these drivers prior to 1981 are responsible for the remaining 65.5% of the accumulated sink from 1981 to 2016. These results refine the attribution of the land sink to the various drivers and would help constrain prognostic models that often have large uncertainties in simulating changes in vegetation and their impacts on the global carbon cycle.

Growth of tetragonal BaTiO3 single crystal fibers

1986 ◽  
Vol 1 (3) ◽  
pp. 452-456 ◽  
Author(s):  
M. Saifi ◽  
B. Dubois ◽  
E.M. Vogel ◽  
F.A. Thiel
Keyword(s):  
Barium Titanate ◽  
Single Crystal ◽  
Optical Fibers ◽  
Amorphous Materials ◽  
Telecommunication Network ◽  
Ferroelectric Materials ◽  
Ferroelectric Crystal ◽  
Sintered Ceramic ◽  
Active Devices ◽  
Crystal Fibers

With the increasing use of optical fibers in the telecommunication network, there is need for fiber geometry compatible optical devices such as optical amplifiers, switches, couplers, and isolators. These active devices are based on field-dependent material properties, such as electrooptic and magneto-optic effects, which are stronger in single crystal than in amorphous materials. Single crystal fibers can be grown by the laser heated pedestal growth (LHPG) technique. In this paper we report the growth of single crystal fibers of ferroelectric barium titanate from sintered ceramic rods of stoichiometric barium titanate. Barium titanate is one of the most extensively investigated ferroelectric materials. However, its growth from stoichiometric melt always results in its hexagonal nonferroelectric phase. Using LHPG, single crystal strontium titanate seed, and sintered ceramic barium titanate rods, we have succeeded in growing single crystal fibers (∼ 100 μ m diameter) of pure barium titanate with tetragonal (ferroelectric) crystal structure. This paper discusses growth and characterization of these fibers.

Perpetual Crisis: The Politics of Saving the ABC

2000 ◽  
Vol 94 (1) ◽  
pp. 105-116 ◽  
Author(s):  
Geoffrey Craig
Keyword(s):  
Structural Change ◽  
Government Funding ◽  
Democratic Politics ◽  
Public Issue ◽  
Public Broadcaster ◽  
A Site ◽  
Funding Cuts

In recent years there has been a rally to ‘save’ the Australian Broadcasting Corporation (ABC). This paper explores the assumptions about the national broadcaster which often inform such rescue attempts. The ABC seems to have entered a state of ‘perpetual crisis ‘following government funding cuts, political accusations of bias, issues of structural change and the Mansfield inquiry. Even more than usual, the identity, functions and future of the national broadcaster have become a public issue. While fully supporting a strong national public broadcaster as a space for public contestation, I argue that saving the ABC should not render it ‘safe’, returning it to some prior privileged state and established identity. Rather, drawing on an ‘agonistic model of democratic politics’. I argue that the ABC needs to be conceptualised as a site which produces ‘dilemmatic space’ and that the crises of the ABC are those which necessarily constitute the institution as a public broadcaster.

Effect of proximity of buloke (Allocasuarina luehmannii) trees on buloke early sapling survival in a semiarid environment

2013 ◽  
Vol 61 (4) ◽  
pp. 302 ◽  
Author(s):  
John W. Morgan ◽  
Paulius A. Kviecinskas ◽  
Martine Maron
Keyword(s):  
Plant Communities ◽  
Agricultural Intensification ◽  
Agricultural Land ◽  
Mature Trees ◽  
Semiarid Environment ◽  
Dramatic Decline ◽  
Negative Effect ◽  
Sapling Survival ◽  
Soil Conductivity ◽  
A Site

Agricultural intensification has led to the dramatic decline of buloke (Allocasuarina luehmannii) and the plant communities it dominates in southern Australia. Conservation of remnant buloke woodlands and revegetation of agricultural land are both required for the persistence and improved ecological function of this threatened community. We examined the effect of proximity of mature buloke trees on early sapling survival, to provide guidelines for revegetation aimed at enhancing degraded remnants. We planted buloke saplings at different distances from the base of remnant mature trees at a site in western Wimmera, Victoria, with and without herbaceous competition. Mature buloke trees altered most soil nutrients (positively), soil water content (negatively) and soil conductivity (positively) at different gradients from the tree base, depending on the factor measured. Mature buloke trees had a strong negative effect on conspecific sapling survival in the first summer after planting in both the presence and absence of an herbaceous understorey, possibly because of the strong effect of trees on soil moisture. Competition from mature buloke was high nearest to the trees (up to 9 m from tree base), but competition from the native understorey also appeared important for saplings in the tree gaps, as evidenced by their improved survival when the understorey was removed. We suggest that to establish buloke saplings in areas where mature trees already occur (i.e. enhancement plantings around isolated paddock trees), planting tubestock outside the canopy of mature buloke is necessary to enhance establishment success.

Prediction of ferroelectricity in recent Inorganic Crystal Structure Database entries under space group Pba2

1996 ◽  
Vol 52 (5) ◽  
pp. 806-809 ◽  
Author(s):  
S. C. Abrahams ◽  
K. Mirsky ◽  
R. M. Nielson
Keyword(s):  
Crystal Structure ◽  
Curie Temperature ◽  
Spontaneous Polarization ◽  
Ferroelectric Materials ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Atomic Coordinates ◽  
Crystal Structure Database

Three new entries in space group Pba2 in the 1995 edition of the Inorganic Crystal Structure Database have been examined in the light of previously developed criteria for the prediction of ferroelectricity. The structural prediction [Abrahams (1989). Acta Cryst. B45, 228–232] that seven of the 21 entries presented under this space group in the 1988 edition most likely corresponded to previously unrecognized ferroelectric materials is thereby updated. The atomic coordinates of [(NH2)2C(NHNH3)]ZrF6, among the new entries, are shown to satisfy the structural criteria; the maximum displacement along the polar axis required of any atom to undergo spontaneous polarization reversal is no larger than ~ 0.9 Å for a C or N atom and ~ 1.4 Å for a H atom, within the aminoguanidinium (2+) cation. By contrast, all atoms in the two independent ZrF6 anions are within 0.1 Å of an arrangement with zero spontaneous polarization. The characteristic force constant of the organic group is presently unknown, hence the Curie temperature for the crystal cannot be estimated. In the second new entry, the only atoms in the structure of the superconductor Ba0.6K0.4BiO23 at 403 K which depart significantly from a centrosymmetric arrangement are three of the four independent O atoms, one of which is at a site only 6% occupied. If these displacements are not artefacts, then this material is ferroelectric with an estimated Curie temperature in the range 410–740 K; a subsequent study, however, reported the structure in space group Pbam. The atomic coordinates of the final 1995 entry, (Cl3PNPCl3)(MoOCl4), do not differ significantly from centrosymmetry, in which case the material is not ferroelectic, apart from unequal occupancy of the Mo-atom sites. If the disorder model is correct and the two Mo sites are unequally occupied, then these sites cannot become equivalent and (Cl3PNPCl3)(MoOCl4) must remain polar without the possibility of becoming ferroelectric.

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