scholarly journals Spin-Phonon Coupling in A2BMnO6 (A = La, Pr, Nd, Sm, Gd; B = Co, Ni) Double-Perovskite Thin Films: Impact of the A-Site Cation Radius

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 747
Author(s):  
Christoph Meyer ◽  
Philipp Ksoll ◽  
Vladimir Roddatis ◽  
Vasily Moshnyaga
Keyword(s):  
Lattice Structure ◽  
Double Perovskite ◽  
Aerosol Deposition ◽  
Lattice Parameter ◽  
Strong Impact ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Cation Radius ◽  
A Site ◽  
The Impact

Two series of B-site ordered, double-perovskite A2CoMnO6 and A2NiMnO6 (A = La, Pr, Nd, Sm, Gd) epitaxial films with thickness d ~ 100 nm were grown on SrTiO3(111) substrates via metalorganic aerosol deposition. Polarization and temperature-dependent Raman spectroscopy were carried out in order to determine the spin-phonon coupling constant, λ, and the impact of the A-site cation radius on the phonon properties. The reduction of the A-site cation radius from La3+ down to Gd3+ systematically shifts the Raman modes to lower wavenumbers, and decreases the magnetization-induced softening of the Ag breathing mode, described by the spin-phonon coupling constant, λ, which changes from λ = 1.42 cm−1 (La2CoMnO6) and λ = 1.53 cm−1 (La2NiMnO6) down to λ = 0.58 cm−1 (Gd2CoMnO6) and λ = 0.44 cm−1 (Gd2NiMnO6). A similar effect of the A-cation radius was established for the c-lattice parameter and Curie temperature, TC, in this series of double-perovskite films. Our observations directly demonstrate a strong impact of the lattice structure on the ferromagnetic superexchange interaction in double perovskites. Moreover, the A2CoMnO6 and A2NiMnO6 series exhibit very similar behavior of spin-phonon coupling due to the only moderate difference of Co2+ and Ni2+ cation size.

scholarly journals Geometric Analysis and Formability of the Cubic A2BX6 Vacancy Ordered Double Perovskite Structure

2020 ◽  
Author(s):  
Anjie Cheng ◽  
Chenyang Lyu ◽  
Tianyi Shi ◽  
Ziheng Wang ◽  
Robert Palgrave
Keyword(s):  
Geometric Analysis ◽  
Double Perovskite ◽  
Lattice Parameter ◽  
Inorganic Crystal Structure Database ◽  
The Best Approximation ◽  
Sphere Approximation ◽  
Fixed Radius ◽  
A Site ◽  
Crystal Structure Database ◽  
Correct Size

<p>A geometric analysis of the cubic A<sub>2</sub>BX<sub>6</sub> structure commonly formed by metal halides is presented. Using the ‘hard sphere’ approximation, where the ions are represented by spheres of a fixed radius, we derive four limiting models that each constrain the distances between constituent ions in different ways. We compare the lattice parameters predicted by these four models with experimental data from the Inorganic Crystal Structure Database (ICSD). For the fluorides, the maintenance of the AX bond length at the sum of the A and X radii gives the best approximation of the lattice parameter, leading to structures with widely separated BX<sub>6</sub> octahedra. For the heavier halides, a balance between forming an A site cavity of the correct size, and maintaining suitable anion-anion distances determines the lattice parameter. It is found that in many A<sub>2</sub>BX<sub>6</sub> compounds of heavier halides, the neighbouring octahedra show very significant anion-anion overlap, meaning that the commonly used description of these materials of having isolated BX<sub>6</sub> octahedra is misleading. We use the geometric models to derive formability criteria for vacancy ordered double perovskites. </p>

Cation Site Mixing for Strain Relief in Three-Layer Aurivillius Ceramics

2002 ◽  
Vol 755 ◽  
Author(s):  
Michael S. Haluska ◽  
Scott T. Misture
Keyword(s):  
Rietveld Analysis ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Cation Site ◽  
X Ray ◽  
Earth Cation ◽  
Cation Radius ◽  
Bond Valence Sum ◽  
Average Size ◽  
A Site

ABSTRACTThree-layer Aurivillius ceramics Bi2SrCaNb2TiO12, Bi2Sr1.5Ca.5Nb2TiO12, Bi2Sr2Nb2TiO12, Bi2Sr1.5Ba.5Nb2TiO12, Bi2SrBaNb2TiO12 were formed via solid-state synthesis and their structures characterized by Rietveld analysis of powder x-ray diffraction data. Site mixing was observed for all species with the largest amount of mixing occurring in Bi2SrBaNb2TiO12. Bond valence sum calculations (BVS) showed that the A-site BVS increased from underbonded in the Bi2SrCaNb2TiO12 composition to overbonded in Bi2SrBaNb2TiO12. The A-site BVS increased linearly with lattice parameter and average A-site cation radius. Bi-site position relaxation was observed as the average size of the alkaline earth cation on the Bi-site increased. Site mixing occurs in these compounds in order to relieve interlayer strain between the (Bi2O2)2+ layer and the perovskite blocks, between the Nb and Ti-layers of the perovskite blocks, and to reduce the BVS of the perovskite A-site.

scholarly journals Geometric Analysis and Formability of the Cubic A2BX6 Vacancy Ordered Double Perovskite Structure

2020 ◽  
Author(s):  
Anjie Cheng ◽  
Chenyang Lyu ◽  
Tianyi Shi ◽  
Ziheng Wang ◽  
Robert Palgrave
Keyword(s):  
Geometric Analysis ◽  
Double Perovskite ◽  
Lattice Parameter ◽  
Inorganic Crystal Structure Database ◽  
The Best Approximation ◽  
Sphere Approximation ◽  
Fixed Radius ◽  
A Site ◽  
Crystal Structure Database ◽  
Correct Size

<p>A geometric analysis of the cubic A<sub>2</sub>BX<sub>6</sub> structure commonly formed by metal halides is presented. Using the ‘hard sphere’ approximation, where the ions are represented by spheres of a fixed radius, we derive four limiting models that each constrain the distances between constituent ions in different ways. We compare the lattice parameters predicted by these four models with experimental data from the Inorganic Crystal Structure Database (ICSD). For the fluorides, the maintenance of the AX bond length at the sum of the A and X radii gives the best approximation of the lattice parameter, leading to structures with widely separated BX<sub>6</sub> octahedra. For the heavier halides, a balance between forming an A site cavity of the correct size, and maintaining suitable anion-anion distances determines the lattice parameter. It is found that in many A<sub>2</sub>BX<sub>6</sub> compounds of heavier halides, the neighbouring octahedra show very significant anion-anion overlap, meaning that the commonly used description of these materials of having isolated BX<sub>6</sub> octahedra is misleading. We use the geometric models to derive formability criteria for vacancy ordered double perovskites. </p>

PHOTOINDUCED IR ABSORPTION IN AMnO3 AS A FUNCTION OF THE A SITE IONIC SPECIES

2000 ◽  
Vol 14 (29n31) ◽  
pp. 3590-3595 ◽  
Author(s):  
T. MERTELJ ◽  
M. HROVAT ◽  
D. KUSCER ◽  
D. MIHAILOVIC
Keyword(s):  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Ionic Species ◽  
Ir Absorption ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Photoinduced Absorption ◽  
Polaron Hopping ◽  
Electron Phonon Coupling ◽  
A Site

A comparison of photoinduced absorption spectra in AMnO 3 with A = La 3+, Nd 3+, Ca 2+ is presented. The spectra are analyzed in the framework of photon assisted polaron hopping. In contrast to LaMnO 3 and NdMnO 3 the photoinduced absorption spectrum of CaMnO 3 shows distinct contributions from photoexcited holes and electrons. Both contributions are identified, and our results imply that magnitude of electron-phonon coupling constant for electrons in Mn eg orbitals in CaMnO 3 is significantly smaller than in LaMnO 3.

scholarly journals A Quantum–Mechanical Study of Clean and Cr–Segregated Antiphase Boundaries in Fe3Al

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 3954 ◽  
Author(s):  
Martin Friák ◽  
Monika Všianská ◽  
Mojmír Šob
Keyword(s):  
Magnetic Properties ◽  
Magnetic Moments ◽  
Lattice Parameter ◽  
Quantum Mechanical ◽  
Strong Impact ◽  
Antiphase Boundaries ◽  
Cubic Symmetry ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
The Impact

We present a quantum-mechanical study of thermodynamic, structural, elastic, and magnetic properties of selected antiphase boundaries (APBs) in Fe 3 Al with the D0 3 crystal structure with and without Cr atoms. The computed APBs are sharp (not thermal), and they have {001} crystallographic orientation. They are characterized by a mutual shift of grains by 1/2⟨100⟩a where a is the lattice parameter of a cube-shaped 16-atom elementary cell of Fe 3 Al, i.e., they affect the next nearest neighbors (APB-NNN type, also called APB-D0 3 ). Regarding clean APBs in Fe 3 Al, the studied ones have only a very minor impact on the structural and magnetic properties, including local magnetic moments, and the APB energy is rather low, about 80 ± 25 mJ/m 2 . Interestingly, they have a rather strong impact on the anisotropic (tensorial) elastic properties with the APB-induced change from a cubic symmetry to a tetragonal one, which is sensitively reflected by the directional dependence of linear compressibility. The Cr atoms have a strong impact on magnetic properties and a complex influence on the energetics of APBs. In particular, the Cr atoms in Fe 3 Al exhibit clustering tendencies even in the presence of APBs and cause a transition from a ferromagnetic (Cr-free Fe 3 Al) into a ferrimagnetic state. The Fe atoms with Cr atoms in their first coordination shell have their local atomic magnetic moments reduced. This reduction is synergically enhanced (to the point when Fe atoms are turned non-magnetic) when the influence of clustering of Cr atoms is combined with APBs, which offer specific atomic environments not existing in the APB-free bulk Fe 3 Al. The impact of Cr atoms on APB energies in Fe 3 Al is found to be ambiguous, including reduction, having a negligible influence or increasing APB energies depending on the local atomic configuration of Cr atoms, as well as their concentration.

Fictive Fathers in the Field

2020 ◽  
Vol 1 (3) ◽  
pp. 265-273
Author(s):  
Katrina Daly Thompson
Keyword(s):  
Cultural Studies ◽  
Ethnographic Research ◽  
A Site ◽  
The Impact

Through my own narrative about my relationship with my fictive father in Zanzibar and the impact of this relationship on my research, in this autoethnographic essay I explore three themes: fictiveness, fatherhood, and the field. These themes tie together different aspects of the term “patriography,” linking them to ethnography and its subgenre autoethnography. Drawing on the term “patriography” as the science or study of fathers, I use the concept of “the field” to examine the impact of narratives about fathers on not only the field as a site of ethnographic research but also on the field of African cultural studies.

When Do Psychopathic Traits Affect Cooperative Behavior?: An Iterated Prisoner's Dilemma Experimental Study

2020 ◽  
Author(s):  
M Testori ◽  
M Kempf ◽  
RB Hoyle ◽  
Hedwig Eisenbarth
Keyword(s):  
Prisoner's Dilemma ◽  
Cooperative Behavior ◽  
Prisoner’S Dilemma ◽  
Selection Procedure ◽  
Psychopathic Traits ◽  
Strong Impact ◽  
Iterated Prisoner's Dilemma ◽  
Human Decision ◽  
The Impact ◽  
Iterated Prisoner’S Dilemma

© 2019 Hogrefe Publishing. Personality traits have been long recognized to have a strong impact on human decision-making. In this study, a sample of 314 participants took part in an online game to investigate the impact of psychopathic traits on cooperative behavior in an iterated Prisoner's dilemma game. We found that disinhibition decreased the maintenance of cooperation in successive plays, but had no effect on moving toward cooperation after a previous defection or on the overall level of cooperation over rounds. Furthermore, our results underline the crucial importance of a good model selection procedure, showing how a poor choice of statistical model can provide misleading results.

The Impact of Economic Crisis on Tourism Industry: A Bangladesh Perspective

2016 ◽  
Vol 2 (1) ◽  
Author(s):  
Md. Ziaul Haque
Keyword(s):  
Economic Crisis ◽  
Tourism Industry ◽  
Political Crisis ◽  
Strong Impact ◽  
Negative Consequences ◽  
Policy Makers ◽  
Tourism Product ◽  
International Tourist ◽  
Sustained Recovery ◽  
The Impact

The tourism sector is experiencing numerous challenges as a result of the global economic crisis. After a significant contraction in 2009, tourism rebounded strongly  in  2010  and  in  2011  the  international  tourist  arrivals  and  receipts  are projected to increase substantially. The Tourism industry is expected to show a sustained recovery in 2012. The crisis has particularly strong impact and slightly negative consequences in Bangladesh. The country is undergoing a political crisis, as well, and it seems that the forthcoming elections may be the only solution for the restoration of stability and social peace.  In addition, tourism can be the driving force behind Bangladesh economic recovery. However, for its achievement the country’s policy makers should take several measures towards restructuring and improving the sector. These measures include: enhancement of alternative forms of tourism; environmental protection; creation of quality infrastructure; and boost of competitiveness through a tourism product that offers value for money

The Impact Of Economic Crisis On Tourism Industry: A Bangladesh Perspective

2015 ◽  
Vol 1 (1) ◽  
pp. 15
Author(s):  
Md. Ziaul Haque
Keyword(s):  
Economic Crisis ◽  
Tourism Industry ◽  
Political Crisis ◽  
Strong Impact ◽  
Negative Consequences ◽  
Policy Makers ◽  
Tourism Product ◽  
International Tourist ◽  
Sustained Recovery ◽  
The Impact

The tourism sector is experiencing numerous challenges as a result of the global economic crisis. After a significant contraction in 2009, tourism rebounded strongly  in  2010  and  in  2011  the  international  tourist  arrivals  and  receipts  are projected to increase substantially. The Tourism industry is expected to show a sustained recovery in 2012. The crisis has particularly strong impact and slightly negative consequences in Bangladesh. The country is undergoing a political crisis, as well, and it seems that the forthcoming elections may be the only solution for the restoration of stability and social peace.  In addition, tourism can be the driving force behind Bangladesh economic recovery. However, for its achievement the country’s policy makers should take several measures towards restructuring and improving the sector. These measures include: enhancement of alternative forms of tourism; environmental protection; creation of quality infrastructure; and boost of competitiveness through a tourism product that offers value for money

Static and dynamic response of sandwich beams with lattice and pantographic cores

2021 ◽  
pp. 109963622110338
Author(s):  
Yury Solyaev ◽  
Arseniy Babaytsev ◽  
Anastasia Ustenko ◽  
Andrey Ripetskiy ◽  
Alexander Volkov
Keyword(s):  
Mechanical Performance ◽  
Lattice Structure ◽  
Unit Length ◽  
Experimental Tests ◽  
Plane Geometry ◽  
Sandwich Beams ◽  
Static Tests ◽  
Three Point Bending ◽  
The Core ◽  
The Impact

Mechanical performance of 3d-printed polyamide sandwich beams with different type of the lattice cores is investigated. Four variants of the beams are considered, which differ in the type of connections between the elements in the lattice structure of the core. We consider the pantographic-type lattices formed by the two families of inclined beams placed with small offset and connected by stiff joints (variant 1), by hinges (variant 2) and made without joints (variant 3). The fourth type of the core has the standard plane geometry formed by the intersected beams lying in the same plane (variant 4). Experimental tests were performed for the localized indentation loading according to the three-point bending scheme with small span-to-thickness ratio. From the experiments we found that the plane geometry of variant 4 has the highest rigidity and the highest load bearing capacity in the static tests. However, other three variants of the pantographic-type cores (1–3) demonstrate the better performance under the impact loading. The impact strength of such structures are in 3.5–5 times higher than those one of variant 4 with almost the same mass per unit length. This result is validated by using numerical simulations and explained by the decrease of the stress concentration and the stress state triaxiality and also by the delocalization effects that arise in the pantographic-type cores.

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