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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (31 December 2017) | Viewed by 31261

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Dr. Edmondo Gilioli

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IMEM-CNR, (Institute of Materials for Electronic and Magnetism – National Research Council), Parco Area delle Scienze 37/A, 43124 Parma, Italy
Interests: CIGS-based solar cells; thin film deposition; high pressure synthesis (HP/HT)
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Dr. Francesco Mezzadri

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Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A - 43124 Parma, Italy
Interests: crystallography; phase transitions; solid state chemistry; multiferroic materials

Special Issue Information

Dear Colleagues,

Since its birth, crystallography has played a central role in the development of new knowledge, both as a support to other disciplines and in its primary role of revealing the structure of materials, to which most of the properties at the solid state are related. The application of external stimuli (e.g., pressure, temperature, electromagnetic waves, reactive atmosphere, etc.) allows a deeper insight into the behavior of materials in unconventional, in some case extreme, environments, enabling a better understanding of the physics and chemistry of matter in standard conditions.

Nowadays, facilities for the application of non-ambient conditions are easily accessible in many laboratories and an increasing number of studies are unveiling the correlation between the material structure and the external stumuli, both for fundamental research and for practical applications.

The Special Issue on "Non-Ambient Cystallography" aims to gather the innovative achievements of this vast and interdisciplinary community.

Dr. Edmondo Gilioli
Dr. Francesco Mezzadri
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

Pressure/Temperature dependent crystallography
Experiments under extreme conditions
Phase transitions
In-situ crystallography
Applied electro-magnetic fields

Published Papers (7 papers)

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Research

17 pages, 20828 KiB

Open AccessArticle

P-T Phase Diagram of LuFe₂O₄

by Maria Poienar, Julie Bourgeois, Christine Martin, Maryvonne Hervieu, Françoise Damay, Gaston Garbarino, Michael Hanfland, Thomas Hansen, François Baudelet, Jean Louis Bantignies, Patrick Hermet, Julien Haines and Jérôme Rouquette

Crystals 2018, 8(5), 184; https://doi.org/10.3390/cryst8050184 - 24 Apr 2018

Cited by 2 | Viewed by 4212

Abstract

The high-pressure behavior of LuFe₂O₄ is characterized based on synchrotron X-ray diffraction and neutron diffraction, resistivity measurements, X-ray absorption spectroscopy and infrared spectroscopy studies. The results obtained enabled us to propose a P-T phase diagram. In this study, the low pressure charge-ordering melting could be detected by synchrotron XRD in the P-T space. In addition to the ambient pressure monoclinic C2/m and rhombohedral R

\bar{3}

m phases, the possible P

\bar{1}

triclinic phase, the monoclinic high pressure form Pm and metastable modulated monoclinic phases were observed; the latter modulated monoclinic phases were not observed in the present neutron diffraction data. Furthermore, the transition to the Pm phase which was already characterized by strong kinetics is found to be favored at high temperature (373 K). Based on X-ray absorption spectroscopy data the Pm phase, which could be recovered at atmospheric pressure, can be explained by a change in the Fe-local environment from a five-fold coordination to a distorted 5 + 1 one. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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10 pages, 2347 KiB

Open AccessArticle

Temperature-Induced Reversible and Irreversible Transitions between Metastable Perovskite Phases in the BiFe_1−ySc_yO₃ Solid Solutions

by Andrei N. Salak, Dmitry D. Khalyavin, Edwin Eardley, Nikolai M. Olekhnovich, Anatoli V. Pushkarev, Yury V. Radyush, Aleksandr D. Shilin and Vasili V. Rubanik

Crystals 2018, 8(2), 91; https://doi.org/10.3390/cryst8020091 - 10 Feb 2018

Cited by 3 | Viewed by 3164

Abstract

The antipolar orthorhombic Pnma phase with the

\sqrt{2} a_{p} \times 4 a_{p} \times 2 \sqrt{2} a_{p}

superstructure (a_p ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO₃. Temperature-induced [...] Read more.

The antipolar orthorhombic Pnma phase with the

\sqrt{2} a_{p} \times 4 a_{p} \times 2 \sqrt{2} a_{p}

superstructure (a_p ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO₃. Temperature-induced structural transformations in metastable perovskite solid solutions with the Pnma structure corresponding to the range of 0.30 ≤ y ≤ 0.60 of the (1−y)BiFeO₃-yBiScO₃ quasi binary system were studied using temperature X-ray and neutron powder diffraction. These compositions cannot be prepared in bulk form at ambient pressure but can be stabilized in the Pnma phase by means of quenching after synthesis under high pressure. The compositions were investigated in situ between 1.5 K and the temperature of the stability limit of their metastable phases (about 870–920 K). It has been found that heating the as-prepared compositions with the Pnma phase leads to formation of the rhombohedral R3c phase (

\sqrt{2} a_{p} \times \sqrt{2} a_{p} \times 2 \sqrt{3} a_{p}

), which, on cooling down to room temperature, either remains or transforms into a polar orthorhombic Ima2 phase (

2 a_{p} \times \sqrt{2} a_{p} \times \sqrt{2} a_{p}

). The observed phase transformations in the BiFe_1−ySc_yO₃ perovskite series on heating and on cooling are considered in terms of geometrical factors. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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10 pages, 5612 KiB

Open AccessArticle

Coupling between Spin and Charge Order Driven by Magnetic Field in Triangular Ising System LuFe₂O_4+δ

by Lei Ding, Fabio Orlandi, Dmitry D. Khalyavin, Andrew T. Boothroyd, Dharmalingam Prabhakaran, Geetha Balakrishnan and Pascal Manuel

Crystals 2018, 8(2), 88; https://doi.org/10.3390/cryst8020088 - 06 Feb 2018

Cited by 4 | Viewed by 5074

Abstract

We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe₂O_4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel temperature (T_N = 240 K) indicates that LuFe₂O_4+δ shows short-range, two-dimensional (2D) correlations in the FeO₅ triangular layers, characterized by the development of a magnetic scattering rod along the 1/3 1/3 L direction, persisting down to 5 K. We also found that on top of the 2D correlations, a long range ferromagnetic component associated with the propagation vector k₁ = 0 sets in at around 240 K. On the other hand, an external magnetic field applied along the c-axis effectively favours a three-dimensional (3D) spin correlation between the FeO₅ bilayers evidenced by the increase of the intensity of satellite reflections with propagation vector k₂ = (1/3, 1/3, 3/2). This magnetic modulation is identical to the charge ordered superstructure, highlighting the field-promoted coupling between the spin and charge degrees of freedom. Formation of the 3D spin correlations suppresses both the rod-type diffuse scattering and the k₁ component. Simple symmetry-based arguments provide a natural explanation of the observed phenomenon and put forward a possible charge redistribution in the applied magnetic field. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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11 pages, 2280 KiB

Open AccessArticle

High Pressure Induced Insulator-to-Semimetal Transition through Intersite Charge Transfer in NaMn₇O₁₂

by Davide Delmonte, Francesco Mezzadri, Fabio Orlandi, Gianluca Calestani, Yehezkel Amiel and Edmondo Gilioli

Crystals 2018, 8(2), 81; https://doi.org/10.3390/cryst8020081 - 03 Feb 2018

Cited by 3 | Viewed by 3405

Abstract

The pressure-dependent behaviour of NaMn₇O₁₂ (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18 GPa, accompanied by a change in the compressibility of the system. On the other hand, the crystallographic determinations rule out a symmetry change to be at the origin of the transition, despite all the structural parameters pointing to a symmetrizing effect of pressure. Bond valence sum calculations indicate a charge transfer from the octahedrally coordinated manganese ions to the square planar ones, likely favouring the delocalization of the carriers. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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8 pages, 3579 KiB

Open AccessArticle

Pressure-Induced Transformation of Graphite and Diamond to Onions

by Vladimir D. Blank, Valentin D. Churkin, Boris A. Kulnitskiy, Igor A. Perezhogin, Alexey N. Kirichenko, Sergey V. Erohin, Pavel B. Sorokin and Mikhail Yu. Popov

Crystals 2018, 8(2), 68; https://doi.org/10.3390/cryst8020068 - 31 Jan 2018

Cited by 22 | Viewed by 5603

Abstract

In this study, we present a number of experiments on the transformation of graphite, diamond, and multiwalled carbon nanotubes under high pressure conditions. The analysis of our results testifies to the instability of diamond in the 55–115 GPa pressure range, at which onion-like structures are formed. The formation of interlayer sp³-bonds in carbon nanostructures with a decrease in their volume has been studied theoretically. It has been found that depending on the structure, the bonds between the layers can be preserved or broken during unloading. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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15 pages, 6074 KiB

Open AccessArticle

Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO₂ System at High Pressure

by Alwin James, M. Mahdi Davari Esfahani, William R. Woerner, Alexandra Sinclair, Lars Ehm, Artem R. Oganov and John B. Parise

Crystals 2018, 8(2), 15; https://doi.org/10.3390/cryst8020015 - 23 Jan 2018

Cited by 5 | Viewed by 5435

Abstract

We employed ab initio evolutionary algorithm USPEX to speed up the discovery of a novel oxynitride in the binary system of GaN-TiO₂ using high-pressure synthesis. A 1:2 mixture of GaN and nanocrystalline TiO₂ (anatase) was reacted under 1 GPa of pressure and at 1200 °C in a piston cylinder apparatus to produce a mixture of TiO₂ (rutile) and an unknown phase. From the initial analysis of high resolution neutron and X-ray diffraction data, it is isomorphic with monoclinic V₂GaO₅ with a unit cell composition of Ga₁₀Ti₈O₂₈N₂ with the following parameters: monoclinic, space group C2/m, a = 17.823(1) Å, b = 2.9970(1) Å, c = 9.4205(5) Å, β = 98.446(3)°; Volume = 497.74(3) Å³. Further, a joint rietveld refinement revealed two distinct regimes—A Ti-rich block and a Ga-rich block. The Ti-rich block consists of four edge-shared octahedra and contains a site which is about 60% occupied by N; this site is bonded to four Ti. The remainder of the block consists of edge linked Ti-octahedral chains linked to the TiN/TiO fragments at octahedral corners partially occupied by nitrogen. The Ga-block contains two symmetry independent octahedral sites, occupied mostly by Ga, and a pure Ga-centered tetrahedral site bonded mostly to oxygen. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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1771 KiB

Open AccessArticle

Influence of External Static Magnetic Fields on Properties of Metallic Functional Materials

by Xiaowei Zuo, Lin Zhang and Engang Wang

Crystals 2017, 7(12), 374; https://doi.org/10.3390/cryst7120374 - 13 Dec 2017

Cited by 9 | Viewed by 3819

Abstract

Influence of external static magnetic fields on solidification, solid phase transformation of metallic materials have been reviewed in terms of Lorentz force, convection, magnetization, orientation, diffusion, and so on. However, the influence of external static magnetic fields on properties of metallic functional materials is rarely reviewed. In this paper, the effect of static magnetic fields subjected in solidification and/or annealing on the properties of Fe–Ga magnetostrictive material, high strength high conductivity Cu-based material (Cu–Fe and Cu–Ag alloys), and Fe–Sn magnetic material were summarized. Both the positive and negative impacts from magnetic fields were found. Exploring to maximize the positive influence of magnetic fields is still a very meaningful and scientific issue in future. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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