S. Yáñez-Vilar

Bio: S. Yáñez-Vilar is an academic researcher from University of Santiago de Compostela. The author has contributed to research in topics: Dielectric & Perovskite (structure). The author has an hindex of 17, co-authored 41 publications receiving 1199 citations. Previous affiliations of S. Yáñez-Vilar include University of A Coruña & University of Porto.

Characterization of the Order−Disorder Dielectric Transition in the Hybrid Organic−Inorganic Perovskite-Like Formate Mn(HCOO)3[(CH3)2NH2]

Abstract: We have found that the hybrid organic-inorganic perovskite-like formate Mn(HCOO)(3)[(CH(3))(2)NH(2)] shows a dielectric transition around 190 K. According to single crystal X-ray diffraction, the compound shows rhombohedral symmetry at room temperature and monoclinic symmetry at low temperature (100 K), and the main difference between both structures is that the (CH(3))(2)NH(2)(+) (DMA) cations are disordered in the high temperature phase but cooperatively ordered in the low temperature one. The vibrational spectra of this compound reveal that significant changes take place in the vibrations ascribed to the DMA cation (changes in the frequency of certain vibrations, splitting of particular vibrations, and changes in the intensities), while no significant changes have been observed in those attributed to the formate anion. On the basis of all this information, we attribute the origin of the dielectric transition to the dynamics of the DMA cations: above 190 K these cations can rotate inside the cubooctahedral cavity created by the [Mn(HCOO)(3)](-) framework, while for lower temperatures such rotation gets frozen, and their cooperative arrangement inside the cavities give rise to the observed dielectric transition.

Multiferroic behavior in the double-perovskite Lu 2 MnCoO 6

Abstract: We present Lu${}_{2}$MnCoO${}_{6}$, a multiferroic member of the double perovskites that we have investigated using x-ray and neutron diffraction, specific heat, magnetization, electric polarization, and dielectric constant measurements This material possesses a net electric polarization strongly coupled to a net magnetization below 35 K, despite the antiferromagnetic ordering of the $S=3/2$ Mn${}^{4+}$ and Co${}^{2+}$ spins in an $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ configuration along the $c$ direction We discuss the magnetic order in terms of a condensation of domain boundaries between $\ensuremath{\uparrow}\ensuremath{\uparrow}$ and $\ensuremath{\downarrow}\ensuremath{\downarrow}$ ferromagnetic domains, with each domain boundary producing an electric polarization due to spatial inversion symmetry breaking In an applied magnetic field the domain boundaries slide, controlling the size of the magnetization, electric polarization, and magnetoelectric coupling

Near room temperature dielectric transition in the perovskite formate framework [(CH3)2NH2][Mg(HCOO)3].

Abstract: We report that the hybrid organic–inorganic compound [(CH3)2NH2][Mg(HCOO)3] shows a marked dielectric transition around Tt ∼ 270 K, associated to a structural phase transition from SG Rc (centrosymmetric) to Cc (non-centrosymmetric). This is the highest Tt reported so far for a perovskite-like formate that is thus a promising candidate to display electric order very close to room temperature.

First-order structural transition in the multiferroic perovskite-like formate [(CH3)2NH2][Mn(HCOO)3]

Abstract: In this work we explore the overall structural behaviour of the [(CH3)2NH2][Mn(HCOO)3] multiferroic compound across the temperature range where its ferroelectric transition takes place by means of calorimetry, thermal expansion measurements and variable temperature powder and single crystal X-ray diffraction. The results clearly prove the presence of a structural phase transition at Tt ~ 187 K (the temperature at which the dielectric transition occurs) that involves a symmetry change from Rc to Cc, twinning of the crystals, a discontinuous variation of the unit cell parameters and unit cell volume, and a sharp first-order-like anomaly in the thermal expansion. In addition, the calorimetric results show a 3-fold order–disorder transition. The calculated pressure dependence of the transition temperature is rather large (dTt/dP = 4.6 ± 0.1 K kbar−1) in that it should be feasible to shift it to room temperature under adequate thermodynamic conditions, for instance by application of an external pressure.

Cobalt-catalyzed sulfate radical-based advanced oxidation: A review on heterogeneous catalysts and applications

Abstract: Recently sulfate radical-based advanced oxidation processes (SR-AOPs) attract increasing attention due to their capability and adaptability in decontamination. The couple of cobalt and peroxymonosulfate (PMS) is an efficient way to produce reactive sulfate radicals. This article reviews the state-of-the-art progress on various heterogeneous cobalt-based catalysts for PMS activation, including cobalt oxides, cobalt-ferrite and supported cobalt by diverse substrates. We summarize the intrinsic properties of these catalysts and their fundamental behaviors in PMS activation, as well as synthetic approaches. In addition, influencing factors and synergistic techniques of Co/PMS systems in organic degradation and possible environmental applications are also discussed. Finally, we propose perspectives on challenges related to cobalt-based catalysts, heterogeneous Co/PMS systems and their potential applications in practical environmental cleanup.

Defect‐Engineered Metal–Organic Frameworks

Abstract: Defect engineering in metal–organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of “defect-engineering” concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs.

Chemically diverse and multifunctional hybrid organic–inorganic perovskites

Abstract: Hybrid organic–inorganic perovskites (HOIPs) can have a diverse range of compositions including halides, azides, formates, dicyanamides, cyanides and dicyanometallates. These materials have several common features, including their classical ABX3 perovskite architecture and the presence of organic amine cations that occupy the A-sites. Current research in HOIPs tends to focus on metal halide HOIPs, which show promise for use in solar cells and optoelectronic devices; however, the other subclasses also exhibit a diverse range of physical properties. In this Review, we summarize the chemical variability and structural diversity of all known HOIP subclasses. We also present a comprehensive account of their intriguing physical properties, including photovoltaic and optoelectronic properties, dielectricity, magnetism, ferroelectricity, ferroelasticity and multiferroicity. Moreover, we discuss the current challenges and future opportunities in this exciting field. Hybrid organic–inorganic perovskites (HOIPs) comprise a diverse range of chemical compositions from halides and azides to formates, dicyanamides, cyanides and dicyanometallates. In this Review, advances in the synthesis, structures and properties of all HOIP subclasses are summarized and their future opportunities are discussed.