Repositório Comunidade: CDF_FMNCCDF_FMNChttps://hdl.handle.net/1822/18892024-03-19T11:47:27Z2024-03-19T11:47:27ZBi2ZnTiO6 thin films for next-generation photovoltaics: study of material properties characterization and deposition conditions optimizationFigueiras, F. G.Fernandes, J. R. A.Silva, José Pedro BastoAlikin, D. O.Lourenço, A. C.Tavares, P. B.https://hdl.handle.net/1822/875412023-12-14T11:33:20ZTítulo: Bi2ZnTiO6 thin films for next-generation photovoltaics: study of material properties characterization and deposition conditions optimization
Autor: Figueiras, F. G.; Fernandes, J. R. A.; Silva, José Pedro Basto; Alikin, D. O.; Lourenço, A. C.; Tavares, P. B.
Resumo: The perovskite-like oxide Bi2ZnTiO6 (BZT) combines a narrow band gap with significant ferroelectric polarization, key parameters for the development of next-generation photovoltaic devices. Nevertheless, BZT remains a relatively unexplored material due to its difficult synthesis. The present experimental work unfolds and optimizes the deposition of BZT phase thin films by rf-sputtering method on standard Pt(111)/TiO2/SiO2/Si(001) substrates. The series of thin films explores different deposition conditions: Substrate temperature (350º-600ºC), RF power (50–80 W), exposure time (30–120 min), O2:Ar ratio (25–50%) and thermal treatments (air-O2). Thin films deposited between 350 and 475ºC are mainly amorphous. Above 490–550ºC the films show incipient crystallization. Depositions at temperatures above 600ºC and heat treatments resulted in partial recrystallization of spurious Bi- or Zn-rich oxides and aurivillius or pyrochlore-like phases. At 550 ºC, the films are dominated by a polycrystalline BZT phase in P4mm tetragonal structure, and the increase of the O2:Ar ratio contributes to improve the B-site order. Not least, no significant structural changes were observed after ∼3 years ageing. Diffuse reflectance measurements show relatively narrow optical band gaps between 1.4–1.9 eV within expected values for this system. Piezo-force microscopy revealed domains contrast and hysteresis loops correlated with the quality of the film crystallized BZT phase.
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<b>Tipo</b>: articleDisentangling stress and strain effects in ferroelectric HfO2Song, TingfengLenzi, VenieroSilva, José Pedro BastoMarques, L.Fina, IgnasiSánchez, Florenciohttps://hdl.handle.net/1822/875402024-01-30T17:47:54ZTítulo: Disentangling stress and strain effects in ferroelectric HfO2
Autor: Song, Tingfeng; Lenzi, Veniero; Silva, José Pedro Basto; Marques, L.; Fina, Ignasi; Sánchez, Florencio
Resumo: Ferroelectric HfO2 films are usually polycrystalline and contain a mixture of polar and nonpolar phases. This challenges the understanding and control of polar phase stabilization and ferroelectric properties. Several factors, such as dopants, oxygen vacancies, or stress, among others, have been investigated and shown to have a crucial role on optimizing the ferroelectric response. Stress generated during deposition or annealing of thin films is a main factor determining the formed crystal phases and influences the lattice strain of the polar orthorhombic phase. It is difficult to discriminate between stress and strain effects on polycrystalline ferroelectric HfO2 films, and the direct impact of orthorhombic lattice strain on ferroelectric polarization has yet to be determined experimentally. Here, we analyze the crystalline phases and lattice strain of several series of doped HfO2 epitaxial films. We conclude that stress has a critical influence on metastable orthorhombic phase stabilization and ferroelectric polarization. On the contrary, the lattice deformation effects are much smaller than those caused by variations in the orthorhombic phase content. The experimental results are confirmed by density functional theory calculations on HfO2 and Hf0.5Zr0.5O2 ferroelectric phases.
<b>Tipo</b>: articleElectrical properties of flexible ceramicsKiran Kumar, N. S.Jayakrishnan, A. R.Rugmini, R.Silva, José Pedro BastoPereira, MárioSugumaran, SathishSekhar, K. C.https://hdl.handle.net/1822/874422023-12-05T10:36:21ZTítulo: Electrical properties of flexible ceramics
Autor: Kiran Kumar, N. S.; Jayakrishnan, A. R.; Rugmini, R.; Silva, José Pedro Basto; Pereira, Mário; Sugumaran, Sathish; Sekhar, K. C.
Resumo: Flexible ceramics subsume all the functional properties of bulk ceramics, but in a format that has been modified to withstand mechanical contorts. Understanding the mechanism of electrical properties as a function of mechanical deformations such as bending, stretching, etc. is critical to optimize the device performance. This chapter presents a comprehensive collection of various electrical properties such as dielectric, piezoelectric, pyroelectric, ferroelectric, electrochemical, and the transport mechanisms of various flexible ceramic films. The realization of these properties into corresponding applications in the realm of energy storage, energy harvesting, data storage, and sensing to develop future generation smart electronic devices is also discussed.
<b>Tipo</b>: bookPartEffect of MgO doping on energy storage and electrocaloric properties of ferroelectric 0.6Ba(Zr0.2Ti0.8)O3–0.4(Ba0.7Ca0.3)TiO3 ceramicsKumar, N. S.KiranJayakrishnan, A. R.Silva, José Pedro BastoSekhar, K. C.https://hdl.handle.net/1822/874372023-12-04T18:45:51ZTítulo: Effect of MgO doping on energy storage and electrocaloric properties of ferroelectric 0.6Ba(Zr0.2Ti0.8)O3–0.4(Ba0.7Ca0.3)TiO3 ceramics
Autor: Kumar, N. S.Kiran; Jayakrishnan, A. R.; Silva, José Pedro Basto; Sekhar, K. C.
Resumo: This study highlights the effect of MgO doping on microstructure, dielectric, ferroelectric, energy storage and electrocaloric properties of lead-free (1-x)(0.6Ba(Zr0.2Ti0.8)O3–0.4(Ba0.7Ca0.3)TiO3)–xMgO ceramics with x varying from 0-5%. X-ray diffraction studies revealed that BZCT-MgO ceramics exhibited a morphotropic phase boundary (MPB), i.e. coexistence of both tetragonal and rhombohedral phases at room temperature for x ≤ 1%. Scanning electron microscope (SEM) images revealed that grain size is decreased with the increase of MgO content. The Raman analysis and temperature dependent dielectric studies further confirm the MPB behaviour at low MgO content. Besides, the MgO additive improves the diffused phase transition (DPT) behaviour of BZCT ceramics, lowers transition temperature and enhances their relaxor behaviour. It is observed that 0.99BZCT–0.01MgO showed optimum energy storage properties with a recoverable energy density of 177.6 mJ/cm3 and an efficiency of 79% at an electric field of 45 kV/cm. Moreover, they exhibited a robust energy storage performance even after passing 107 cycles. Further, the electrocaloric temperature change and responsivity are found 1.12 K at 45 kV/cm and 0.024 Kcm/kV, respectively in 0.99BZCT–0.01MgO ceramics.
<b>Tipo</b>: articleDisentangling the role of the SnO layer on the pyro-phototronic effect in ZnO-based self-powered photodetectorsVieira, E. M. FSilva, José Pedro BastoGwozdz, KatarzynaKaim, AdrianGomes, Nuno M.Chahboun, AdilGomes, M. J. M.Correia, José H.https://hdl.handle.net/1822/874362023-12-14T12:42:08Z2023-12-04T18:40:04ZTítulo: Disentangling the role of the SnO layer on the pyro-phototronic effect in ZnO-based self-powered photodetectors
Autor: Vieira, E. M. F; Silva, José Pedro Basto; Gwozdz, Katarzyna; Kaim, Adrian; Gomes, Nuno M.; Chahboun, Adil; Gomes, M. J. M.; Correia, José H.
Resumo: Self-powered photodetectors (PDs) have been recognized as one of the developing trends of next-generation optoelectronic devices. Herein, it is shown that by introducing a thin layer of SnO film between the Si substrate and the ZnO film, the self-powered photodetector Al/Si/SnO/ZnO/ITO exhibits a stable and uniform violet sensing ability with high photoresponsivity and fast response. The SnO layer introduces a built-in electrostatic field to highly enhance the photocurrent by over 1000%. By analyzing energy diagrams of the p-n junction, the underlying physical mechanism of the self-powered violet PDs is carefully illustrated. A high photo-responsivity (R) of 93 mA W-1 accompanied by a detectivity (D*) of 3.1 x 10(10) Jones are observed under self-driven conditions, when the device is exposed to 405 nm excitation laser wavelength, with a laser power density of 36 mW cm(-2) and at a chopper frequency of 400 Hz. The Si/SnO/ZnO/ITO device shows an enhancement of 3067% in responsivity when compared to the Al/Si/ZnO/ITO. The photodetector holds an ultra-fast response of approximate to 2 mu s, which is among the best self-powered photodetectors reported in the literature based on ZnO.
<b>Tipo</b>: article2023-12-04T18:40:04Z