Influence of the Chemical Pressure on the Magnetic Properties of the Mixed Anion Cuprates Cu2OX2 (X = Cl, Br, I)

International audienceIn this study, we theoretically investigate the structural, electronic and magnetic properties of the Cu2OX2 (X = Cl, Br, I) compounds. Previous studies reported potential spin-driven ferroelectricity in Cu2OCl2, originating from a non-collinear magnetic phase existing below TN ∼70 K. However, the nature of this low-temperature magnetic phase is still under debate. Here, we focus on the calculation of J exchange couplings and enhance knowledge in the field by (i) characterizing the low-temperature magnetic order for Cu2OCl2 and (ii) evaluating the impact of the chemical pressure on the magnetic interactions, which leads us to consider the two new phases Cu2OBr2 and Cu2OI2. Our ab initio simulations notably demonstrate the coexistence of strong anti-ferromagnetic and ferromagnetic interactions, leading to spin frustration. The TN Néel temperatures were estimated on the basis of a quasi-1D AFM model using the ab initio J couplings. It nicely reproduces the TN value for Cu2OCl2 and allows us to predict an increase of TN under chemical pressure, with TN = 120 K for the dynamically stable phase Cu2OBr2. This investigation suggests that chemical pressure is an effective key factor to open the door of room-temperature multiferroicity. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Titanium oxides and silicates as high-kappa dielectrics: A first-principles investigation

Using density functional theory, we investigate the structural, vibrational, and dielectric properties of titanium oxides and silicates, which have attracted considerable attention in the framework of the quest for alternative high-K materials. For the oxides,. three crystalline phases of titanium dioxide are considered. The first two are hypothetical; they are obtained by similarity with the cubic and tetragonal structure of zirconia ZrO2 or hafnia HfO2. The third is the rutile, a crystal that occurs naturally. For the silicates, we analyze a hypothetical TiSiO4 structure constructed by analogy with crystalline ZrSiO4 and HfSiO4 (zircon and hafnon). (C) 2004 Wiley Periodicals, Inc

Beryllocene-like in solid state chemistry: The Η1,Η6 coordination of beryllium ions in graphite-analogue BeB2C2

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High potential positive materials for lithium-ion batteries: transition metal phosphates

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Mechanics and physics of a glass/particles photonic sponge

International audienceA glass containing mechanoluminescent crystalline particles behaves as a photonic sponge: that is to say it fills up with trapped electrons when exposed to UV light, and it emits light when submitted to a mechanical loading, similar to a sponge soaked with water that is wringed under mechanical action! A major finding of the present study is that the elasto-mechanoluminescence effect showing up on unloading is governed by the deviatoric part of the applied stress (no effect under hydrostatic pressure). Furthermore, the structural source for this phenomenon was elucidated by a detailed density functional theory analysis of the e(-) energetics at the possible oxygen vacancy sites within the crystalline phase. Both the e(-) trapping and detrapping processes under load could be explained. An analogy with hydraulic circuits and the rheology of viscoelastic media was successfully introduced to pave the way to a constitutive law for the mechano-optical coupling phenomenon