F.C. Correia

University of Minho

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Carlos J. Tavares

University of Minho

Joana M. Ribeiro

University of Minho

J. B. Sousa

Administração Regional de Saúde de Lisboa e Vale do Tejo

L. Morellón

Universidad de Zaragoza

M.E. Braga

Indonesia Open University

P. A. Algarabel

Universidad de Zaragoza

Adélio Mendes

Universidade do Porto

M. R. Ibarra

Universidad de Zaragoza

J. P. Araújo

Universidade do Porto

Aleksandr Kalinko

Paderborn University

Cooperative Institutions

University of Minho

Universidade do Porto

University of Lisbon

University of Aveiro

Centre National de la Recherche Scientifique

Faculdade de Tecnologia e Ciências

Instituto Superior Técnico

Universidad de Zaragoza

Instituto de Nanociencia y Materiales de Aragón

Consejo Superior de Investigaciones Científicas

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Transport and magnetic study of the spin reorientation transition in the Tb₅(Si_0.5Ge_0.5)₄magnetocaloric compound

Journal of Physics Condensed Matter (2005)

J. P. Araújo André M. Pereira M.E. Braga R.P. Pinto J. M. Teixeira

Detailed measurements of the electrical resistivity ?(T), thermopower S(T) and magnetization of Tb5(Si0.5Ge0.5)4 in the vicinity of the spin reorientation transitions observed in this compound are reported. Our results indicate a complex spin reorientation process associated with three different lattice sites occupied by the Tb ions. We identify two critical transition temperatures: one at TSR1 = 57?K, as previously reported, and a new one at TSR2 = 40?K. A simple model based on an approximate magnetic anisotropy energy is presented; it gives a satisfactory qualitative description of the main features of the reorientation processes.

Magnetic refrigeration

10.1088/0953-8984/17/32/008

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Citations (18)

Synthesis of Bi2O3/TiO2 nanostructured films for photocatalytic applications

Ceramics International (2018)

F.C. Correia Maria Clara Calheiros Juliana Marques Joana M. Ribeiro Carlos J. Tavares

Bismuth

Methylene blue

10.1016/j.ceramint.2018.09.040

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Citations (42)

The Influence of Sb Doping on the Local Structure and Disorder in Thermoelectric Zno:Sb Thin Films

SSRN Electronic Journal (2022)

Joana M. Ribeiro Frederico J. Rodrigues F.C. Correia Inga Pudza Alexei Kuzmin

Thermoelectric transparent ZnO:Sb thin films were deposited by magnetron sputtering, with Sb content varying between 2-14 at.%. As evidenced from X-ray diffraction analysis, the films crystallize in the ZnO wurtzite structure for lower levels of Sb-doping, developing a degree of amorphization for higher levels of Sb-doping. Temperature-dependent (10-300 K) X-ray absorption spectroscopy studies of the produced thin films were performed at the Zn and Sb K-edges to shed light on the influence of Sb doping on the local atomic structure and disorder in the ZnO:Sb thin films. The analysis of the Zn K-edge EXAFS spectra by the reverse Monte Carlo method allowed to extract detailed and accurate structural information in terms of the radial and bond angle distribution functions. The obtained results suggest that the introduction of antimony to the ZnO matrix promotes static disorder, which leads to the partial amorphization with very small crystallites (~3 nm) for large (12-14 at.%) Sb content. Rutherford backscattering spectrometry (RBS) experiments enabled the determination of the in-depth atomic composition profiles of the films. The film composition at the surfaces determined by X-ray photoelectron spectroscopy (XPS) matches that of the bulk determined by RBS, except for higher Sb-doped ZnO films, where the concentration of oxygen determined by XPS is lower near the surface, possibly due to the formation of oxygen vacancies that lead to an increase in electrical conductivity. Traces of Sb-Sb metal bonds were found by XPS for the sample with the highest level of Sb-doping. Time-of-flight secondary ion mass spectrometry obtained an Sb/Zn ratio that follows that of the film bulk determined by RBS, although Sb is not always homogeneous, with samples with lower Sb content (2 and 4 at.% of Sb) showing a higher Sb content closer to the film/substrate interface. From the optical transmittance and reflectance curves, it was determined that the films with the lower amount of Sb doping have higher band-gaps, in the range of 2.9 – 3.2 eV, while the partially amorphous films with higher Sb content have lower band-gaps in the range of 1.6-2.1 eV. Albeit the short-range crystalline order (~3 nm), the films with 12 at.% of Sb have the highest Seebeck coefficient (~56 μV/K) and a thermoelectric power factor of ~0.2 mW·K-2·m-1.

10.2139/ssrn.4289932

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Multi-step and anomalous reproducible behaviour of the electrical resistivity near the first-order magnetostructural transition of Gd₅(Si_0.1Ge_0.9)₄

Journal of Physics Condensed Matter (2005)

J. B. Sousa André M. Pereira F.C. Correia J. M. Teixeira J. P. Araújo

Very detailed measurements of the electrical resistivity of Gd5(Si0.1Ge0.9)4 are here reported, with special emphasis on the vicinity of the first-order (magnetostructural) martensitic transition which occurs at K. The data cover more than fifty thermal cycles spanning the temperature ranges of 300–10 K (long cycles) and 105–10 K (short cycles). In the initial 10–300 K cycles the martensitic transition takes place in three closely-spaced steps, with associated resistance (R) discontinuities and large thermal hysteresis. In a subsequent series of short cycles (10–105 K) a unique transition occurs, exhibiting a common and quite reproducible R(T) behaviour within a small temperature range ( K) below TS, either in heating or cooling runs. Remarkably, this 'local reproducibility' (within ΔT) remains in spite of the significant resistance changes which occur outside the ΔT-range under thermal cycling. In particular the residual resistance systematically increases under thermal cycling, but the corresponding effect is absent in the ΔT temperature range. This excludes microcracking as a dominant resistive mechanism in our results, pointing to an intrinsic character of the reproducible behaviour just below TS. We also analyse the R(T) behaviour when changing from long to short thermal cycles, and the R(T) evolution towards a reversible final behaviour, after extended thermal cycling.

Temperature cycling

Classification of discontinuities

Hysteresis

Atmospheric temperature range

Thermal hysteresis

10.1088/0953-8984/17/15/017

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Citations (14)

Transparent niobium-doped titanium dioxide thin films with high Seebeck coefficient for thermoelectric applications

Surface and Coatings Technology (2021)

Joana M. Ribeiro F.C. Correia Fábio Rodrigues J. S. Reparaz A. R. Goñi

Thermoelectric generator

Figure of Merit

10.1016/j.surfcoat.2021.127724

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Citations (6)

Measuring the impact of green retrofits on CO$_2$ emissions: London Housing Case Study

arXiv (Cornell University) (2023)

F.C. Correia M. Fazion

The residential sector is responsible for approximately 20 percent of the world's energy-related greenhouse gas emissions. In order to improve this reality, it is essential to help and support the leading actor in this scene, the homeowner. In general, buildings are complex objects as each home may have very particular parameters: different materials (windows, walls, types of roofs, etc.), uses, and habits. No two cases are identical. In this paper, we addressed this problem by proposing a method to obtain estimates of energy and carbon savings resulting from a class of retrofit projects and housing profiles. We applied our formulas to conduct a case study of the London residential sector, supported by the publicly available Energy Performance Certificates (EPC) dataset. As a result of a multi-project renovation of a house, including loft insulation, double-glazed windows, and energy-efficient lighting (LED), we found that the average family in the Greater London area could save approximately 9 MWh in energy consumption, 1,700 kgCO$_2$ in carbon emissions and more than GBP 800 on the energy bills, over a year, in contrast to a cost of around GBP 9,000 (or a return on investment of 11 years). In another example, applying the method to calculate what is needed to install heat pumps in each house in London, a total of GBP 16.9 billion would be spent, leading to savings of GBP 450 million per year (return on investment of 37 years). Finally, an overall upgrade to loft insulation would cost London households GBP 1.4 billion, generating GBP 290 million in annual savings (a 5-year return on investment).

Investment

Upgrade

Single-family detached home

Consumption

10.48550/arxiv.2310.07444

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Citations (0)

XPS analysis of ZnO:Ga films deposited by magnetron sputtering: Substrate bias effect

Applied Surface Science (2018)

F.C. Correia N. Bundaleski Orlando M.N.D. Teodoro M. R. Correia L. Rebouta

Wurtzite crystal structure

Biasing

10.1016/j.apsusc.2018.07.135

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Citations (50)

Thermopower behavior in the Gd5(Si0.1Ge0.9)4 magnetocaloric compound from 4 to 300 K

Journal of Applied Physics (2002)

J. B. Sousa M.E. Braga F.C. Correia F. Carpinteiro L. Morellón

Recent studies on the orthorhombic Gd5(Si0.1Ge0.9)4 compound show, upon heating, a ferromagnetic to antiferromagnetic-like (AFM*) transition at TS=78 K, coupled with a first-order structural martensitic transformation keeping the orthorhombic symmetry but producing a large increase in the interlayer Si(Ge) distances leading to covalent bond-pair breaking. A second-order AFM*→(paramagnetic)PM transition occurs at TN=125 K. We report thermopower (S) measurements for the Gd5(SixGe1−x)4 series, performed on an x=0.1 sample, from 4 to 300 K, with increasing and decreasing temperatures through successive thermal cycling. Resistivity measurements show a systematic increase in the residual resistivity and a dramatic change in the ρ(T) behavior upon thermal cycling. In spite of this, the thermopower data show a common intrinsic behavior both in the ferromagnetic phase (T<TS=78 K) and above ∼230 K, i.e., independent of the number of thermal cycles, increasing or decreasing temperature, and of the particular residual resistivity. Also no drastic differences are seen in S(T) from TS to TN, upon thermal cycling. The structural transition is marked (upon heating) by a sharp increase in the S magnitude, reaching a deep negative minimum of −23 μV K−1 at ∼95 K. Then S(T) rises with increasing slope as T approaches TN, where dS/dT exhibits a singularity. S(T) hysteresis sets in at TS, reaches a maximum around 100 K, does not disapear at TN but persists in the PM phase up to ∼230 K. The later feature correlates well with a similar effect observed in ρ(T). The striking differences between S(T) and ρ(T) behavior under thermal cycling are analyzed.

Magnetic refrigeration

Orthorhombic crystal system

Temperature cycling

Residual resistivity

Hysteresis

10.1063/1.1459612

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Citations (19)

Thermopower and electrical resistivity behavior near the martensitic transition in Gd5(SixGe1−x)4 magnetocaloric compounds

Journal of Magnetism and Magnetic Materials (2004)

R.P. Pinto J. B. Sousa F.C. Correia J. P. Araújo M.E. Braga

Magnetic refrigeration