Artículos (Física de la Materia Condensada)

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Boron nitride nanosheets as an effective strategy against the slow crack growth and hydrothermal ageing in zirconia composites
(Elsevier, 2025-06-18) Muñoz Ferreiro, Carmen; Morales Rodríguez, Ana; Reveron, H.; Guisado Arenas, Elisa; Cottrino, S.; Moreno, P.; Prada Rodrigo, J.; Chevalier, J.; Gallardo López, Ángela María; Poyato, Rosalía; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; European Union (UE)
This paper explores the effectiveness of boron nitride nanosheets in preventing the premature failure of yttria-stabilized tetragonal zirconia ceramics, particularly in humid environments. A simple, low-cost and scalable technique -shear exfoliation in a kitchen blender- was used to prepare BNNS, and pure zirconia and composites with 1, 2.5 and 5 vol. % BNNS were spark plasma sintered. Accelerated hydrothermal ageing experiments in autoclave revealed a remarkable improvement of low temperature degradation resistance in all the composites. Fracture toughness and slow crack growth of the composites with 1 and 2.5 vol. % BNNS were evaluated by bending tests performed in notched specimens. Although the composites presented fracture toughness values similar to those of the reference zirconia, an increase of ∼18 % on crack-tip toughness was achieved. Similar R-curves evaluated in air and in oil-impregnated 2.5 vol. % BNNS composites revealed a limitation of stress-assisted corrosion by water in zirconia, thanks to the BNNS incorporation.
Impact of Tb4+ and morphology on the Thermal Evolution of Tb-doped TiO2 Nanostructured Hollow Spheres and Nanoparticles
(Elsevier, 2021-02-05) Colomer, M. T.; Rodríguez, E.; Morán Pedroso, María; Vattier Lagarrigue, María Florencia; Andrés, A. de; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; European Union (UE)
Tb-doped TiO2 hollow spheres (HSs) in the range 0.0-2.0 at.% have been,synthesized by the first time to the best of our knowledge. The HSs are compared with,nanoparticles (NPs) to evaluate the impact of morphology on their physicochemical and,photoluminescence (PL) behavior upon increasing calcination temperature. After,calcination at 550ºC, the particles are anatase with a primary average size of 10.0 ± 0.2,nm for the NPs and 12.0 ± 0.2 nm for those that form the micron sized hollow spheres of,1.8 µm diameter and ca. 64 nm shell thickness. The temperature of the anatase–rutile,transition is found to be strongly dependent on the presence of Tb as well as on,morphology. Contrarily to the usual stabilization of anatase when doping with trivalent,rare-earth ions, the transition temperature is reduced when doping with Tb. The rutile,phase is further favored for the HSs compared to the NPs probably related to the low,density of the HSs and/or a more efficient packing of the nanoparticles that form those,spheres with respect to the packing of the NPs. A slight unit-cell volume decrease for the,anatase structure is observed upon Tb doping, in both the NPs and in the HSs, contrary to,the expected increment due to the larger ionic radius of Tb3+ compared to Ti4+,. In addition,,2,the intensity of the characteristic f-f Tb3+ emission bands is extremely weak both in the,anatase and rutile phases. The transition is accompanied with the emergence of an infrared,emission band centered at 810 nm related to the formation of defects during the structural,transformation providing deep levels in the gap that partly quench the f-f emissions in the,rutile phase. The results are consistent with the presence of Tb in both +3 and +4 valence,states. XPS measurements confirmed the presence of Tb3+ as well as of Tb4+ in both HSs,and NPs with a Tb4+ fraction that increases with increasing Tb doping. The large fraction,of Tb4+ present in the samples originates the weak f-f emission intensity, the slight,decrease of the cell parameters and the destabilization of the anatase phase
Proof of the Nernst theorem
(Springer, 2025-06-13) Martín Olalla, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada;
The Nernst heat theorem is proven from purely thermodynamic arguments connected with the second law of thermodynamics. The proof stipulates that T 0 is formalized by a Carnot thermometer, and is independent of the vanishing of the specific heats, or the unattainability of the zeroth isotherm. With this proof, the second law of thermodynamics would extend its applicability, and the third postulate of thermodynamics would be narrowed to the fact that the entropy of a finite density, chemically homogeneous body must not be negative.
High Piezoelectric Performance in Lead-free BCHT Fine-grained Ceramics Synthesized by Mechanochemistry
(Elsevier, 2025) Santiago Andrades, L.; Romero Landa, Francisco Javier; Gotor, F. J.; Sayagués, M. J.; Moriche Tirado, Rocío; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia, Innovación y Universidades (MICIU). España
Lead-free piezoelectric ceramics (Ba1-xCax) (Ti1-yHfy)O3 with stoichiometries close to the morphotropic phase boundary (MPB) were synthesized by high-energy ball milling. The influence of Hf and Ca contents and the sintering method (conventional and hot-press) on the piezoelectric, dielectric, and ferroelectric response was investigated. It was confirmed that the different phases stabilized at room temperature and the structural distortion are strongly dependent on the stoichiometry. The coexistence of tetragonal, orthorhombic and rhombohedral phases was observed in samples with the lowest Ca and Hf contents. These samples, which are in the MPB region, also showed the greatest structural distortion, resulting in higher values of d33. Samples with lower Hf content exhibited a higher coercive field, remnant polarization, and temperature in the ferroelectric to paraelectric transition. Despite the high sintering temperature leading to high densification, grain growth during sintering was limited because of the use of mechanochemically synthesized powders. Although Ba0.85Ca0.15Hf0.10Ti0.90O3 stoichiometry has been reported in the literature as the best for piezoelectric properties, in this work, BCHT solid solution with the lowest dopant content studied (Ba0.90Ca0.10Hf0.05Ti0.95O3) showed the best combination of functional properties. Ceramics of this composition with grain size <2 μm exhibited a d33 > 250 pC/N, with almost no relaxation after 24 h, and the highest permittivity. In the field of piezoelectric materials, there is considerable interest in reducing grain size while maintaining high piezoelectric performance, as this can lead to improvements in mechanical properties.
Piezoelectric and Dielectric Response of BaTiO3/PVDF-TrFE Composites with High β-Phase Content
(American Chemical Society, 2025) Otero Pino, Andrea; Sayagués, M. J.; Romero Landa, Francisco Javier; Gotor, F. J.; Moriche Tirado, Rocío; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia e Innovación (MICIN). España
The search for flexible piezoelectric materials to build adaptable sensors, electronics, and nanogenerators has becomea key area of interest. The addition of piezoceramic particles to piezoelectric polymers, such as the copolymer poly(vinylidenefluoride-trifluoroethylene) (PVDF-TrFE), is one of the strategies used to enhance the piezoelectric response. In this work, the effectof BaTiO3 content on the β-phase formation, crystallization, and piezoelectric and dielectric properties of the polymer-basedcomposites is investigated. High-energy ball milling was used as an effective, greener technique to achieve well-dispersed mixturescompared to those obtained using organic solvents. During the dispersion process, amorphization and reduction of the crystallinedomain size occur. After compression molding and postprocessing, the crystallinity was recovered and was strongly dependent onthe filler content. Although significant differences in the β-phase fraction were not observed, conformational defects are induced withhigh BaTiO3 contents. The interlayer distances became smaller due to the presence of the ceramic particles after compressionmolding and remained almost unchanged after postprocessing. For the composites, the minimum voltage required to obtain ameasurable piezoelectric coefficient (d33) was significantly reduced compared to neat PVDF-TrFE, even for low contents, which iskey for real applications. Three different piezoelectric behaviors were found depending on the BaTiO3 fraction. For composites with40 vol %, where both matrix and filler contribute to the overall piezoelectric response, the use of a two-step poling method induced asynergistic effect with an increase in d33 of ∼180%. However, the relaxation of the ceramic contribution after 24 h returns the valueof d33 to that obtained by applying a one-step poling strategy.
Pyroelectric Potassium Hydrogen Malate with Polarized Hydrogen Bond Chains and Aligned Dipole Moments
(American Institute of Physics, 2008) de Matos Gomes, E.; Belsley, M. S.; Criado Vega, Alberto; Rodrigues, V. H.; Costa, M. M.R.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Fundação para a Ciência e a Tecnologia. Portugal
A spontaneous polarization of 16 μC/ cm2 at room temperature has been found in the semiorganic crystal potassium hydrogen malate (KHC 4H4O5 · H2O). This high polarization results from a structural arrangement of oriented dipoles formed by the potassium cations and the COO- group from the malate anion, and long hydrogen bonded polarized chains created by the hydrogen L-malate anion via O-H⋯O interactions, directed along the polar sixfold axis. The material shows a second harmonic generation with a rotationally averaged effective second order susceptibility equal to 0.70 of potassium dihydrogen phosphate at an incident wavelength of 1064 nm.
Space- and Time-resolved Emission Features of Micro- and Nano-sized Perylene-based Zr Metal-Organic Frameworks
(2024-10-15) Romero-Muñiz, Ignacio; García Calvo, José; Romero-Muñiz, Carlos; Rodríguez San Miguel, David; Torres, Tomás; Zamora, Félix; Bottari, Giovanni; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Agencia Estatal de Investigación. España; Ministerio de Ciencia e Innovación (MICIN). España; Comunidad Autónoma de Madrid
While many photoresponsive metal‒organic frameworks (MOFs) have been reported to date, finding applications in several technologically relevant fields such as photocatalysis, sensors, and light-emitting devices, significantly scarcer are the reports addressing the relationship between the MOFs emissive features and their crystalline domain size (i.e., micro- and nano-sized materials). Herein, a valuable contribution is offered to this issue which consists of the use of reticular chemistry to prepare a Zr-MOF featuring spatially separated tetracarboxylated-functionalized perylenes as ligand. Single crystal X-ray analysis of such Zr-MOF revealed the formation of micro- and meso-porous channels. The perylene-based Zr-MOF exhibited notable optoelectronic features, including a relatively small optical bandgap of 1.82 eV and emission features different from that of the constituting perylene ligand in the solid state. Additionally, local probe techniques are used to unveil the emission properties of isolated Zr-MOF crystals. Space- and time-resolved fluorescence studies revealed a strong dependence of the emissive features of the Zr-MOF, both in terms of its intensity and lifetime, to the crystalline domain size.
Fabrication of Al2O3-Y3Al5O12-ZrO2 composites by single-step spark plasma sintering
(Elsevier, 2025-03-12) Vakhshouri, Maryam; Talimian, Ali; Najafzadehkhoee, Aliasghar; Gallardo López, Ángela María; Poyato, Rosalía; Gutiérrez Mora, Felipe; Galusek, Dušan; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Union (UE)
Fabricating Al2O3-Y3Al5O12-ZrO2 ceramic composites with a eutectic microstructure is challenging and costly, as it requires high-temperature melting of precursor materials. Here, we report on the successful production of Al2O3-Y3Al5O12- 5 mol% ZrO2 composites with lamellar eutectic microstructure through single-step spark plasma sintering (SPS) of sol-gel synthesized powder. The release of volatile species from partially calcined powders, due to limited calcination at 1000°C for 2 h, as well as their fine particle size, were used to create the conditions for local electric discharge and plasma formation during SPS; this resulted in the local formation of eutectic liquids, enabling the formation of lamellar microstructures. The microstructural features can be tailored by modifying the calcination process.
Diversity and composition of ocular microbiota in contact lens wearers: Efficacy of liposomal ozonated oil
(Elsevier, 2025-06) Sánchez González, María del Carmen; Gallardo Real, Inmaculada; Gutiérrez Sánchez, Estanislao; Hita Cantalejo, María Concepción de; Capote Puente, Raúl; Sánchez González, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Cirugía
Purpose: To characterize the ocular surface microbiota in regular contact lens wearers with dry eyes and assess the effectiveness of reducing bacterial load using a liposomal ozonated oil solution. Methods: This prospective, longitudinal, controlled study randomized subjects into two groups. Group A (45 subjects) received hydroxypropylmethylcellulose (HPMC, Artific®), while Group B (41 subjects) received ozonated sunflower seed oil with soybean phospholipids (OSSO, Ozonest®). Microbial communities were analyzed via DNA metabarcoding of the 16S rRNA gene, and statistical analyses (alpha and beta diversity) were performed in R. Results: Both groups predominantly harbored Staphylococcus caprae, Streptococcus oralis, and Corynebacterium spp., with OSSO and HPMC users showing distinct bacterial profiles. Alpha diversity showed no significant differences, but beta diversity revealed differences in bacterial composition between the groups. Conclusions: The results seem to indicate that the use of ozonized oil reduces the bacterial load compared to the solution used as a control.
Efficacy of eyelid warming devices as first-step treatment in meibomian gland dysfunction: A systematic review with meta-analysis
(Elsevier, 2025-07) Ballesteros Sánchez, Antonio; Rocha de Lossada, Carlos; Sánchez González, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Cirugía
Purpose: To investigate the efficacy of eyelid warming devices as first-step treatment in patients with meibomian gland dysfunction (MGD). Methods: A systematic review with meta-analysis of RCTs, reporting the effects eyelid warming devices in 3 databases, PubMed, Scopus and Web of Science, was performed according to the PRISMA statement. Results: Seven studies including 367 patients, and 440 eyes were analysed. The overall efficacy did not significantly favor either group when comparing eyelid warming devices to the control groups or warm towel compresses, nor between moisture chamber devices and warm compress devices. However, the change in OSDI questionnaire (SMD 0.91; 95 % CI: 0.44 to 1.39; P = 0.0002) and NIBUT (SMD 1.10; 95 % CI: 0.61 to 1.59; P < 0.0001) were significantly favorable for eyelid warming devices compared to the control groups. Similar results were obtained for tear film stability (SMD 0.97; 95 % CI: 0.32 to 1.61; P = 0.003) when comparing eyelid warming devices to warm towel compresses. Specifically, the sensitivity analysis of these groups revealed that changes in OSDI questionnaire (MD 9.41; 95 % CI: 1.70 to 17.13; P = 0.02; I2 = 49 %) and NIBUT (MD 2.24; 95 % CI: 1.20 to 3.28; P < 0.0001; I2 = 71 %) were significantly favorable for eyelid warming devices. When comparing moisture chamber devices and warm compress devices, only the change in TBUT (SMD 0.75; 95 % CI: 0.23 to 1.28; P = 0.005; I2 = 30 %) were significantly favorable for moisture chamber goggles. Conclusions: Despite their limited overall efficacy, eyelid warming devices significantly reduce OSDI questionnaire and improve NIBUT compared to controls or warm towel compress groups. Evidence remains insufficient to confirm whether moisture chamber devices provide better outcomes than warm compress devices. Further well-designed RCTs are needed to confirm these findings.
Outcomes of Corneal Compound Hyperopic Astigmatism With Presbyopia by Zeiss PRESBYOND Laser Blended Vision LASIK Using Default Custom Refractive Software Master Target Refractions for Reduced Anisometropia
(Slack Incorporated, 2024) Hernández Lucena, Julia; Alonso Aliste, Federico; Amián Cordero, Jonatan; Sánchez González, José María; Universidad de Sevilla. Departamento de Física de la Materia Condensada
PURPOSE: To evaluate the effectiveness, safety, and stability of a modified PRESBYOND Laser Blended Vision protocol (Carl Zeiss Meditec AG) for correcting hyperopic astigmatism and presbyopia, using Custom Refractive Software Master (CRSM) targeting over a 6-month period. METHODS: A total of 636 eyes of 318 patients with a mean age of 51.05 ± 4.71 years (range: 40 to 60 years) met the inclusion and exclusion criteria. All patients completed a 6-month follow-up. CRSM software was used to generate ablation profiles for the MEL90 excimer laser (Carl Zeiss Meditec AG). The target refraction was emmetropic for the dominant eyes and between -0.75 and -1.12 diopters (D) for the near eyes. RESULTS: Visual and refractive results were studied separately by the dominant and non-dominant eyes. The mean attempt to correct for spherical equivalent refraction was +2.17 ± 1.16 D (range: -1.00 to +5.37 D). The mean attempted cylinder was -0.60 ± 0.75 D (range: -4.00 to 0.00 D). All eyes monocularly achieved uncorrected distance visual acuity (UDVA) of 20/25 or better after refractive treatment and 88% achieved 20/20. Binocularly all eyes achieved UDVA of 20/25 or better and 96.54% achieved 20/20. Ninety-eight percent of the patients maintained their corrected distance visual acuity before surgery and UDVA 6 months after surgery. CONCLUSIONS: This hyperopic micro-anisometropia protocol with PRESBYOND Laser Blended Vision was an effective, safe, and well-tolerated refractive treatment. It was an effective procedure with excellent results for UDVA and uncorrected near visual acuity and demonstrates that binocular summation exists.
Phase transition behavior in ferroelectric BaTi0.8Zr0.2O3: Evidence of polar cluster reorientation above Curie temperature
(AIP Publishing, 2025-05-27) Aktas, Oktay; Romero Landa, Francisco Javier; He, Zhengwang; Linyu, Gan; Ding, Xiangdong; Martín Olalla, José María; Gallardo Cruz, María del Carmen; Lookman, Turab; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Natural National Science Foundation of China (NSFC); Scientific and Technological Research Council of Turkey (TÜBİTAK)
We study the phase transition behavior of the ferroelectric BaTi0.8Zr0.2O3 in the paraelectric region above the Curie temperature. The investigation of the phase transition using caloric, dielectric, and elastic measurements indicates that the ferroelectric transition at Tc = 292 K is continuous and displays weakly relaxor characteristics. The nonlinear scaling of entropy and polarization, as well as the temperature dependencies of dielectric and elastic properties, indicates the presence of local structures in the paraelectric phase. The non-zero remnant polarization is measured up to a characteristic temperature T* ∼ 350 K. This temperature coincides with the temperature where the dielectric constant deviates from the Curie–Weiss law and is identified as the coherence temperature T*, associated with the formation of static polar nanostructures. Finally, direct current field cooling in the paraelectric phase using fields smaller than the coercive field leads to an elastic response and remnant piezoelectricity below T*, attributed to the re-orientation of polar nanostructures. The observed remnant effect, along with the temperature dependence of the piezoelectric effect and its time dependence below and above T*, is consistent with increased coherence and slower dynamics of these structures on cooling, leading to symmetry-disallowed remnant piezoelectricity due to glassy behavior below T*.
Tuning the Curie Temperature in γ-FeNi Nanoparticles for Magnetocaloric Applications by Controlling the Oxidation Kinetics
(AIP Publishing, 2013) Ucar, Huseyin; Ipus Bados, Jhon Jairo; Laughlin, D. E.; McHenry, M. E.; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Mechanically alloyed Fe70Ni30 and Fe 72Ni28 alloys were characterized in terms of their structural and magnetic properties. Previous studies showed that single phase FCC γ-FeNi alloys with ∼26-30 at. Ni have Curie temperatures, T c, near room temperature. Having Tc near room temperatures along with large magnetization makes γ-FeNi alloys attractive for room temperature magnetocaloric cooling technologies. To obtain a single γ-phase, particles were solution annealed in the γ-phase field and water quenched. The preferential oxidation of Fe during ball milling was used as a means to tune the Curie temperature, Tc, of the alloy. Refrigeration capacities, RCFWHM, of the Fe70Ni 30 and the Fe72Ni28 alloys were calculated to be ≈470 J/kg and 250 J/kg at 5 T, with peak temperatures ≈363 K and ≈333 K, respectively. The RCFWHM for the Fe70Ni 30 is higher than the previously reported Nanoperm (Fe 70Ni30)89Zr7B4 type alloy and on the same order of magnitude with other Fe-based alloys. The maximum magnetic entropy change values observed for the Fe70Ni30 and the Fe72Ni28 are 0.65 and 0.5 J kg-1 K -1, respectively, at a field of 5 T. These are smaller than those of rare earth magnetic refrigerants showing first order transformation behavior. The larger RCFWHM value results mainly from the width of the magnetic entropy curve in these types of materials. We discuss the economic advantage of these rare earth free refrigerants.
The Role of Artificial Intelligence in Optometric Diagnostics and Research: Deep Learning and Time-Series Forecasting Applications
(Multidisciplinary Digital Publishing Institute (MDPI), 2025) Santos, Luis F.F.M.; Sánchez Tena, Miguel Ángel; Álvarez Peregrina, Cristina; Sánchez González, José María; Martínez Pérez, Clara; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Fundação para a Ciência e a Tecnologia. Portugal
This study introduces an Artificial Intelligence framework based on the Deep Learning model Bidirectional Encoder Representations from Transformers framework trained on a dataset from 2000–2023. The AI tool categorizes articles into six classes: Contactology, Low Vision, Refractive Surgery, Pediatrics, Myopia, and Dry Eye, with supervised learning enhancing classification accuracy, achieving F1-Scores averaging 86.4%, AUC at 0.98, Precision at 87%, and Accuracy at 86.8% via one-shot training, while Epoch training showed 85.9% Accuracy and 92.8% Precision. Utilizing the Artificial Intelligence model outputs, the Autoregressive Integrated Moving Average model provides forecasts from all classes through 2030, predicting decreases in research interest for Contactology, Low Vision, and Refractive Surgery but increases for Myopia and Dry Eye due to rising prevalence and lifestyle changes. Stability is expected in pediatric research, highlighting its focus on early detection and intervention. This study demonstrates the effectiveness of AI in enhancing diagnostic precision and strategic planning in optometry, with potential implications for broader clinical applications and improved accessibility to eye care.
The impact of interfacial quality and nanoscale performance disorder on the stability of alloyed perovskite solar cells
(Nature Research, 2024-10-30) Frohna, Kyle; Chosy, Cullen; Al-Ashouri, Amral; Scheler, Florian; Chiang, Yu-Hsien; Dubajic, Milos; Anaya Martín, Miguel; Stranks, Samuel D.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Union (UE). H2020; Engineering Physical Sciences Research Council (EPSCR) U. K.
Microscopy provides a proxy for assessing the operation of perovskite solar cells, yet most works in the literature have focused on bare perovskite thin flms, missing charge transport and recombination losses present in full devices. Here we demonstrate a multimodal operando microscopy toolkit to measure and spatially correlate nanoscale charge transport losses, recombination losses and chemical composition. By applying this toolkit to the same scan areas of state-of-the-art, alloyed perovskite cells before and after extended operation, we show that devices with the highest macroscopic performance have the lowest initial performance spatial heterogeneity—a crucial link that is missed in conventional microscopy. We show that engineering stable interfaces is critical to achieving robust devices. Once the interfaces are stabilized, we show that compositional engineering to homogenize charge extraction and to minimize variations in local power conversion efciency is critical to improve performance and stability. We fnd that in our device space, perovskites can tolerate spatial disorder in chemistry, but not charge extraction.
Revisiting Stability Criteria in Ball-Milled High-Entropy Alloys: Do Hume–Rothery and Thermodynamic Rules Equally Apply?
(Willey, 2024-10-07) Blázquez Gámez, Javier Sebastián; Manchón Gordón, Alejandro F.; Vidal Crespo, Antonio; Caballero Flores, Rafael; Ipus Bados, Jhon Jairo; Conde Amiano, Clara Francisca; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Junta de Andalucía; Universidad de Sevilla
Stability descriptors for the formation of solid solutions can be divided into two categories: inspired by Hume–Rothery rules (HRR) and derived from thermodynamic approaches. Herein, HRRs are extended from binary to high-entropy alloys (HEAs) focusing on compositions prepared by ball milling. Parameters describing stability criteria are interrelated and implicitly account for the microstrains’ storage energy, more determinant than entropy increase in stabilization of HEAs and more effective in bcc structures than close-packed ones (fcc and hcp). An effective temperature, Teff, is defined as the ratio between increase in metallic bonding energy of solid solutions with respect to segregated pure constituents and configurational entropy. This versatile parameter is used as a threshold for stabilization of HEAs at equilibrium and out of equilibrium. When Teff is below room temperature, HEA would be stable at equilibrium. When Teff is below melting temperature, HEA would be obtained by rapid quenching. Limitations related to electronegativity differences remain valid in mechanically alloyed solid solutions. However, ball milling broadens the allowed differences in atomic size to form HEA. Moreover, thermodynamic criteria can be surpassed in these systems, allowing the formation of single-phase solid solutions beyond the compositional range predicted by those criteria.
Magnetostructural transformation and magnetocaloric response in Mn(Fe)NiSi(Al) alloys
(Elsevier, 2024-09-30) Khan, Aun N.; Moreno Ramírez, Luis Miguel; Law, Jia Yan; Franco García, Victorino; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; Oficina de Investigación Científica de la Fuerza Aérea. EE. UU.; European Innovation Council. E. U,
An efficient magnetocaloric refrigerant must have certain characteristics such as a sharp transition near the desired working temperature, a large cyclic magnetocaloric response, and the use of raw materials with reduced costs and low environmental consequences. In this sense, this work focuses on a series of rare-earth- and Co-free Mn0.5Fe0.5NiSi1-xAlx alloys (x = 0.0525, 0.060, 0.0685) with promising magnetocaloric properties. The alloys were synthesized using combined arc melting and induction melting techniques, as this synthesis route provides improved control on the sample composition and homogeneity. We investigated how the heat treatment temperature and Al content affect the magnetostructural and magnetocaloric properties of the alloys. On the one hand, it is found that annealing at 1173 K for 7 days leads to a sharp magnetostructural transformation with no traces of impurities for the alloy with x = 0.0525. Under these conditions, a large isothermal entropy change of –11.5 J kg−1 K−1 for 1 T is obtained near room temperature, significantly improving the value of the as-cast sample. On the other hand, following this optimal heat treatment, the influence of Al content is studied: upon increasing the Al concentration the magnetostructural transformation shifts to lower temperatures, ranging from 320 K for x = 0.0525 to 220 K for x = 0.0685 (measured upon heating).
Interplay between connectivity and passivating agents in perovskite quantum dot networks
(Royal Society of Chemistry, 2024-10-02) Morán Pedroso, María; Tiede, David O.; Romero-Pérez, Carlos; Calvo, Mauricio E.; Galisteo López, Juan F.; Míguez, Hernán; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; Unión Europea NextGeneration; Junta de Andalucía
Introducing quantum dots (QDs) as the active element of an optoelectronic device demands its incorporation in the shape of interconnected arrays that allow for some degree of electronic coupling in order to inject/extract charge carriers. In doing so, beyond reducing the degree of quantum confinement, carriers are exposed to an enhanced defect landscape as they can access adjacent QDs, which is at the origin of the strong reduction of photoluminescence observed in QD solids when compared to that of the isolated QDs. In this work we demonstrate how a proper defect passivating strategy or atmospheric treatment can greatly enhance charge diffusion in a QD film, needed for an optimal carrier injection/extraction demanded for optoelectronic applications, and also improved its stability against external radiation. From a fundamental perspective, we provide evidence showing that trap density distribution, rather than QD size distribution, is mostly responsible for the observed variations in emission decay rates present in the QD networks under analysis.
Influence of the chemical activation with KOH/KNO3 on the CO2 adsorption capacity of activated carbons from pyrolysis of cellulose
(Elsevier, 2024-10-07) Lamata Bermejo, Irene; Alba, María D.; Ramírez Rico, Joaquín; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Junta de Andalucía; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Plant biomass is an attractive precursor to prepare activated carbons with high surface area for CO2 adsorption due to its low-cost and easy regeneration. Despite this interest, there are still remaining questions regarding the optimal processing conditions and the choice of activating agent. Moreover, since plant biomass shows a highly variable proportion of different biopolymers (cellulose, hemicellulose, lignin), it is important to understand the activation effect on each constituent. In this work, carbons obtained from pyrolysis of cellulose were activated using two potassium salts, using two different activation temperatures. The samples were characterized to elucidate the influence of the activation conditions on their CO2 adsorption capacity. In general, all the carbons activated at higher temperature showed higher adsorption capacity. These results are comparable with other carbons derived from biomass described in the bibliography. Among the activated carbons studied, the carbon activated only with KOH exhibits the highest CO2 adsorption capacity at 1 bar meanwhile the highest adsorption capacity at saturation pressure belongs to the carbon activated with larger ratio of KNO3.
Compositional Gradient of Mixed Halide 2D Perovskite Interface Boosts Outdoor Stability of Highly Efficient Perovskite Solar Cells
(Willey, 2023-12-23) Degani, Matteo; Pallotta, Riccardo; Pica, Giovanni; Karimipour, Masoud; Mirabelli, Alessandro; Frohna, Kyle; Anaya Martín, Miguel; Grancini, Giulia; Universidad de Sevilla. Departamento de Física de la Materia Condensada; European Research Council (ERC); European Union (UE). H2020; Engineering and Physical Sciences Research Council (UK)
Interface engineering using self-assembled 2D perovskite interfaces is a consolidated route to efficient and durable perovskite solar cells. Whether the 2D perovskite forms a homogeneous conformal layer or is heterogeneously distributed on the surface, interface defects are passivated, leading to a general improvement in the device's open circuit voltage (VOC) and stability. Here, an innovative strategy is developed for manipulating the composition of the 2D/3D perovskite interface that results in the formation of a gradient halide distribution, which extends from the surface to the bulk. The use of a bromide-based 2D perovskite triggers a progressive Br/I exchange, affecting not only the surface but also the perovskite underneath. As a result, not only the device VOC improve, as expected, but also the photogenerated current is boosted, leading to a device efficiency of up to 24.4%. Such mixed halide gradient effectively passivates surface and bulk defects making the perovskite active layer more efficient and robust, as demonstrated by the superior device stability showing zero losses in performances upon 36 days (more than 800 h) test in outdoor conditions, those ones relevant for a marketable product.

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