Ferroelectric polymorphic phenomena in the layered antiferromagnet Cu(OH)2.

Ferroic orders and their associated structural phase transitions are paramount in the understanding of a multitude of unconventional condensed matter phenomena. On this note, our investigation focuses on the polymorphic ferroelectric (FE) phase transitions of Copper(II) hydroxide, Cu(OH)2, considering an antiferromagnetic ground state. By employing the first-principles studies and group theory analysis, we have provided a systematic theoretical investigation of vibrational properties in the hypotheticalCmcmhigh-symmetry phase to unveil the symmetry-allowed ferroic phases. We identified a non-polar to polar (Cmc21) phase transition, in which the displacive transformation is primarily responsible for the phase change induced by twoB1u(i.e.Γ2-) phonon modes within the centrosymmetric phase. We also observed the existence of two polar structures with the same space group and different degrees of polarization (i.e.Ps= 3.06µC·cm-2andPs= 42.41µC·cm-2), emerging from the high symmetry non-polar structure. According to the structural analysis the FE order, of a geometric nature, is driven by theΓ2-mode in which the O- and H-sites displacements lead the polar distortion with a minor contribution from the Cu-sites. Interestingly, the 3d9:Cu2+Jahn-Teller distortion coupled with the orientational shifts of O-H atoms enhances the polarization.

Anionic nickel and nitrogen effects in the chiral antiferromagnetic antiperovskite Mn3NiN.

Magnetic antiperovskites, having chiral noncollinear antiferromagnetic ordering, have shown remarkable properties that range from negative thermal expansion to anomalous Hall effects. Nevertheless, details on the electronic structure, related to the oxidation states and the octahedral center's site effects, are still scarce. Here, we show a theoretical study, based on first-principles calculations in the framework of density-functional theory (DFT), on the electronic properties associated with the nitrogen site effects on the structural, electronic, magnetic, and topological degrees of freedom. Thus, we show that the nitrogen vacancy increases the value of the anomalous Hall conductivity and retains the chiral Γ4g antiferromagnetic ordering. Moreover, we reveal, based on the Bader charges and the electronic structure analysis, the negative and positive oxidation states of the Ni- and Mn-sites, respectively. This is in agreement with the expected A3α+Bß-Xδ- oxidation states to satisfy charge neutrality in antiperovskites, but the negative charge is rare for transition metals. Finally, we extrapolate our findings on the oxidation states to several Mn3BN compounds, showing that the antiperovskite structure is an ideal platform to encounter negative oxidation states for metals sitting at the corner B-sites.

Lattice dynamics across the ferroelastic phase transition in Ba2ZnTeO6: a Raman and first-principles study.

Structural phase transitions drive several unconventional phenomena including some illustrious ferroic attributes which are relevant for technological advancements. On this note, we have investigated the ferroelastic structural transition of perovskite-type trigonal Ba2ZnTeO6 across Tc ∼ 150 K. With the help of Raman spectroscopy and density-functional theory (DFT)-based calculations, we report new intriguing observations associated with the phase transition in Ba2ZnTeO6. We observed the presence of a central peak (quasi-elastic Rayleigh profile), huge softening in the soft mode, hysteretic phonon behavior, and signatures of coexistent phases. The existence of a central peak in Ba2ZnTeO6 is manifested by a sharp rise in the intensity of the Rayleigh profile concomitant with the huge damping (or softening) of the soft mode (at ∼31 cm-1) near Tc, shedding light on the lattice dynamics during the phase transition. This is further corroborated by our phonon calculations that show that the soft mode (Eg) in the high-symmetry structure involving TeO6 octahedral rotation (with Ba and Zn translation) condenses into Ag and Bg modes in the C2/m low-symmetry phase. While most of the phonon bands split below Tc confirming the phase transition, we observed thermal hysteretic behavior of phonon modes, which signifies the first-order nature of the transition and the presence of coexisting phases as corroborated by our temperature-dependent X-ray diffraction and specific heat measurements.

Unveiling the mechanisms behind the ferroelectric response in the Sr(Nb,Ta)O2N oxynitrides.

Oxynitride perovskites of the type ABO2N have attracted considerable attention thanks to their potential ferroelectric behavior and tunable bandgap energy, making them ideal candidates for photocatalysis processes. Therefore, in order to shed light on the origin of their ferroelectric response, here we report a complete analysis of the structural and vibrational properties of SrNbO2N and SrTaO2N oxynitrides. By employing first-principles calculations, we analyzed the symmetry in-equivalent structures considering the experimentally reported parent I4/mcm space group (with a phase a0a0c- in Glazer's notation). Based on the I4/mcm reference within the 20-atoms unit-cell, we found and studied the ensemble of structures where different octahedral anionic orderings are allowed by symmetry. Thus, by exploring the vibrational landscape of the cis- and trans-type configuration structures and supported by the ionic eigendisplacements and the Born effective charges, we explained the mechanism responsible for the appearance of stable ferroelectric phases in both anionic orderings. The latter goes from covalent-driven in the trans-type ordering to the geometrically-driven in the cis-type configuration. Finally, we found in both cases that the biaxial xy epitaxial strain considerably enhances such ferroelectric response.

Direct Magnetization-Polarization Coupling in BaCuF_{4}.

Herewith, first-principles calculations based on density functional theory are used to describe the ideal magnetization reversal through polarization switching in BaCuF_{4} which, according to our results, could be accomplished close to room temperature. We also show that this ideal coupling is driven by a single soft mode that combines both polarization, and octahedral rotation. The later being directly coupled to the weak ferromagnetism of BaCuF_{4}. This, added to its strong Jahn-Teller distortion and its orbital ordering, makes this material a very appealing prototype for crystals in the ABX_{4} family for multifunctional applications. The described mechanism behaves ideally as it couples the ferroelectric and the magnetic properties naturally and it has not been reported previously.

Electrostatic potential and valence modulation in La0.7Sr0.3MnO3 thin films.

The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1-16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality.

Anharmonic contribution to the stabilization of Mg(OH)2 from first principles.

Geometrical and vibrational characterization of magnesium hydroxide was performed using density functional theory. Four possible crystal symmetries were explored: P3[combining macron] (No. 147, point group -3), C2/m (No. 12, point group 2), P3m1 (No. 156, point group 3m) and P3[combining macron]m1 (No. 164, point group -3m) which are the currently accepted geometries found in the literature. While a lot of work has been performed on Mg(OH)2, in particular for the P3[combining macron]m1 phase, there is still a debate on the observed ground state crystal structure and the anharmonic effects of the OH vibrations on the stabilization of the crystal structure. In particular, the stable positions of hydrogen are not yet defined precisely, which have implications in the crystal symmetry, the vibrational excitations, and the thermal stability. Previous work has assigned the P3[combining macron]m1 polymorph as the low energy phase, but it has also proposed that hydrogens are disordered and they could move from their symmetric position in the P3[combining macron]m1 structure towards P3[combining macron]. In this paper, we examine the stability of the proposed phases by using different descriptors. We compare the XRD patterns with reported experimental results, and a fair agreement is found. While harmonic vibrational analysis shows that most phases have imaginary modes at 0 K, anharmonic vibrational analysis indicates that at room temperature only the C2/m phase is stabilized, whereas at higher temperatures, other phases become thermally competitive.

Room temperature ferroelectricity in fluoroperovskite thin films.

The NaMnF3 fluoride-perovskite has been found, theoretically, to be ferroelectric under epitaxial strain becoming a promising alternative to conventional oxides for multiferroic applications. Nevertheless, this fluoroperovskite has not been experimentally verified to be ferroelectric so far. Here we report signatures of room temperature ferroelectricity observed in perovskite NaMnF3 thin films grown on SrTiO3. Using piezoresponse force microscopy, we studied the evolution of ferroelectric polarization in response to external and built-in electric fields. Density functional theory calculations were also performed to help understand the strong competition between ferroelectric and paraelectric phases as well as the profound influences of strain. These results, together with the magnetic order previously reported in the same material, pave the way to future multiferroic and magnetoelectric investigations in fluoroperovskites.

Strain-Engineered Multiferroicity in Pnma NaMnF_{3} Fluoroperovskite.

In this study we show from first principles calculations the possibility to induce multiferroic and magnetoelectric functional properties in the Pnma NaMnF_{3} fluoroperovskite by means of epitaxial strain engineering. Surprisingly, we found a very strong nonlinear polarization-strain coupling that drives an atypical amplification of the ferroelectric polarization for either compression or expansion of the cell. This property is associated with a noncollinear antiferromagnetic ordering, which induces a weak ferromagnetism phase and makes the strained NaMnF_{3} fluoroperovskite multiferroic. The magnetoelectric response was calculated and it was found to be composed of linear and nonlinear components with amplitudes similar to the ones of Cr_{2}O_{3}. These findings show that it is possible to move the fluoride family toward functional applications with unique responses.

Supervivencia de las paradas cardiacas extrahospitalarias atendidas por una unidad de vigilancia intensiva móvil de Asturias en 2010 / Survival of out-hospital cardiac arrests attended by a mobile intensive care unit in Asturias (Spain) in 2010

Objetivo Determinar los tiempos de asistencia, características extrahospitalarias e intrahospitalarias y supervivencia de las paradas cardiacas atendidas por una UVI móvil, al igual que los factores implicados en la supervivencia al ingreso y al alta hospitalaria. Diseño Estudio observacional retrospectivo desde el 1 de enero de 2010 al 31 de diciembre de 2010, con un seguimiento de un año desde la PCR. Ámbito Área sanitaria IV del Principado de Asturias, con 342.020 habitantes en 2010.PacientesSe incluyeron todos los pacientes que sufrieron una PCR en 2010 y fueron atendidos por la UVI móvil. Variables principales Datos demográficos, causa de la PCR, intervención por testigos, tiempos de asistencia y supervivencia al ingreso, al alta y un año después. Resultados Se atendieron un total de 177 paradas cardiacas. En 120 se indicó el soporte vital avanzado (SVA), siendo 66 de ellas (55%) de causa presumiblemente cardiaca. Recuperaron el pulso 63 pacientes (52,5%), llegando 51 de ellos con vida al hospital (42,5%). Se les dio el alta a 13 pacientes (10,8%). Al año 11 (9,2%) seguían vivos y 9 de ellos (7,5%) tenían una cerebral performance category (CPC) de 1. El ritmo inicial de fibrilación ventricular (FV) y los tiempos cortos en la asistencia se relacionaron con la supervivencia. Conclusiones La supervivencia fue superior a la publicada al ingreso al hospital y similar a la del alta. Como factores relacionados se encontraron los tiempos de asistencia y el ritmo inicial. La reanimación por el testigo fue escasa y no se usaron desfibriladores semiautomáticos (DEA) públicos (AU)

Objective To evaluate attendance timings, out- and in-hospital characteristics, and survival of cardiac arrests attended by an advanced life support unit in Asturias (Spain) in 2010. Factors related to survival upon admission and at discharge were also analyzed. Design A retrospective, observational trial was carried out involving a cohort of out-hospital cardiac arrests (OHCA) occurring between 1 January 2010 and 31 December 2010, with one year of follow-up from OHCA. Setting Health Care Area IV of the Principality of Asturias, with a population of 342,020 in 2010.PatientsAll patients with OHCA and attended by an advanced life support unit were considered. Main variables Demographic data, the etiology of cardiac arrest, bystander cardiopulmonary resuscitation (CPR), attendance timings and survival upon admission, at discharge and after one year. Results A total of 177 OHCA were included. Of these, 120 underwent CPR by the advanced life support team. Sixty-six of these cases (55%) were caused by presumed heart disease. A total of 63 patients (52.5%) recovered spontaneous circulation, and 51 (42.5%) maintained circulation upon admission to hospital. Thirteen patients (10.8%) were discharged alive. After one year, 11 patients were still alive (9.2%) - 9 of them (7.5%) with a Cerebral Performance Category (CPC) score of 1. Ventricular fibrillation and short attendance timings were related to increased survival. Conclusions The survival rate upon admission was better than in other series and similar at discharge. Initial rhythm and attendance timings were related. Public automated external defibrillators (AED) were not used, and bystander CPR was infrequent (AU)

[Survival of out-hospital cardiac arrests attended by a mobile intensive care unit in Asturias (Spain) in 2010]. / Supervivencia de las paradas cardiacas extrahospitalarias atendidas por una unidad de vigilancia intensiva móvil de Asturias en 2010.

OBJECTIVE: To evaluate attendance timings, out- and in-hospital characteristics, and survival of cardiac arrests attended by an advanced life support unit in Asturias (Spain) in 2010. Factors related to survival upon admission and at discharge were also analyzed. DESIGN: A retrospective, observational trial was carried out involving a cohort of out-hospital cardiac arrests (OHCA) occurring between 1 January 2010 and 31 December 2010, with one year of follow-up from OHCA. SETTING: Health Care Area IV of the Principality of Asturias, with a population of 342,020 in 2010. PATIENTS: All patients with OHCA and attended by an advanced life support unit were considered. MAIN VARIABLES: Demographic data, the etiology of cardiac arrest, bystander cardiopulmonary resuscitation (CPR), attendance timings and survival upon admission, at discharge and after one year. RESULTS: A total of 177 OHCA were included. Of these, 120 underwent CPR by the advanced life support team. Sixty-six of these cases (55%) were caused by presumed heart disease. A total of 63 patients (52.5%) recovered spontaneous circulation, and 51 (42.5%) maintained circulation upon admission to hospital. Thirteen patients (10.8%) were discharged alive. After one year, 11 patients were still alive (9.2%) - 9 of them (7.5%) with a Cerebral Performance Category (CPC) score of 1. Ventricular fibrillation and short attendance timings were related to increased survival. CONCLUSIONS: The survival rate upon admission was better than in other series and similar at discharge. Initial rhythm and attendance timings were related. Public automated external defibrillators (AED) were not used, and bystander CPR was infrequent.

Daño neurológico en intoxicación por monóxido de carbono / Neurologic damage in carbon monoxide

No disponible

Nuevo modelo para la práctica de cricotirotomía de urgencia / A new model for emergency crycothyrotomy

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Mordeduras por víboras en el Área IV de Asturias / Viper bites in Area IV in Asturias

No disponible

Neurocisticercosis: crisis convulsiva / Neurocisticercosis: convulsive seizure

No disponible

Síndrome de Poland. Presentacíon de un caso. [Poland's syndrome. A case report].

A case of Poland's syndrome in a 19-year-old male is briefly described. This syndrome is characterized by congenital absence of the pectoralis major and minor muscles as well as homolateral brachysyndactyly. The etiology is unknown. Surgical repair is aimed at constructing a functional hand. Chest deformities usually does not require surgery except in cases of lung herniation or breast hypoplasia.