Crystals

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15 pages, 2199 KiB

Open AccessArticle

Cobalt Doping Effects in Zinc Oxide: A Combined Experimental and Ab Initio Approach

by Luciano F. D. Pereira, Wanderson L. Ferreira, Bruno S. Correa, Messias S. Costa, Cleidilane S. Costa, Arnaldo A. M. Filho, Tatiane S. N. Sales, Brianna Bosch-Santos, Juliana Schell, Anastasia Burimova, Rajendra N. Saxena, Gabriel A. Cabrera-Pasca and Artur W. Carbonari

Crystals 2024, 14(1), 51; https://doi.org/10.3390/cryst14010051 - 29 Dec 2023

Cited by 3 | Viewed by 1446

Abstract

In this paper, we investigate the solubility effects of Co in ZnO (Zn_1−xCo_xO, where x = 0, 0.03, 0.05, 0.1, 0.2, 0.25, 0.4, 0.8, and 1) by combining the results of perturbed angular correlation (PAC) spectroscopy using highly diluted [...] Read more.

In this paper, we investigate the solubility effects of Co in ZnO (Zn_1−xCo_xO, where x = 0, 0.03, 0.05, 0.1, 0.2, 0.25, 0.4, 0.8, and 1) by combining the results of perturbed angular correlation (PAC) spectroscopy using highly diluted ¹¹¹Cd as probe nuclei and ab initio calculations based on spin-density functional theory (SDFT). This combined approach enables us to characterize the local structure around Cd ions, where, through PAC technique, it was possible to measure the EFG as a function of temperature and Co concentration and thereby monitor the changes in the structure and the Co solubility threshold in ZnO and the ZnO/CoO/Co₃O₄ mixed phase. The full-potential linear augmented plane wave plus local orbital (APW+lo) formalism were used here to describe the electronic structure of the supercells, including the atomic relaxations. These Ab initio calculations show an interesting behavior of the Cd and Co impurity levels in the band structure of ZnO, which explains the experimental results in terms of the origin of EFG and the evidence of ferromagnetic response. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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13 pages, 2356 KiB

Open AccessArticle

Temperature Dependence of the Hyperfine Magnetic Field at Fe Sites in Ba-Doped BiFeO₃ Thin Films Studied by Emission Mössbauer Spectroscopy

by Juliana Heiniger-Schell, Krish Bharuth-Ram, Kimara Naicker, Vusumuzi Masondo, Thien Thanh Dang, Marianela Escobar, Carlos Díaz-Guerra, Georg Marschick, Hilary Masenda, Haraldur P. Gunnlaugsson, Bingcui Qi, Iraultza Unzueta, Sveinn Ólafsson, Rajdeep Adhikari, Gerrard Peters, Deena Naidoo, Peter Schaaf, Dmitry Zyabkin, Karl Johnston, Sven Becker and Gerhard Jakob Show full author list Hide full author list

Crystals 2023, 13(5), 724; https://doi.org/10.3390/cryst13050724 - 25 Apr 2023

Viewed by 1868

Abstract

Emission ⁵⁷Fe Mössbauer spectroscopy (eMS), following the implantation of radioactive ⁵⁷Mn⁺ ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO₃ (BFO) thin films. ⁵⁷Mn β decays (t [...] Read more.

Emission ⁵⁷Fe Mössbauer spectroscopy (eMS), following the implantation of radioactive ⁵⁷Mn⁺ ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO₃ (BFO) thin films. ⁵⁷Mn β decays (t_1/2 = 90 s) to the 14.4 keV Mössbauer state of ⁵⁷Fe, thus allowing online eMS measurements at a selection of sample temperatures during Mn implantation. The eMS measurements were performed on two thin film BFO samples, 88 nm and 300 nm thick, and doped to 15% with Ba ions. The samples were prepared by pulsed laser deposition on SrTiO₃ substrates. X-ray diffraction analyses of the samples showed that the films grew in a tetragonal distorted structure. The Mössbauer spectra of the two films, measured at absorber temperatures in the range 301 K–700 K, comprised a central pair of paramagnetic doublets and a magnetic sextet feature in the wings. The magnetic component was resolved into (i) a component attributed to hyperfine interactions at Fe³⁺ ions located in octahedral sites (B_hf); and (ii) to Fe³⁺ ions in implantation induced lattice defects, which were characterized by a distribution of the magnetic field B_Distr. The hyperfine magnetic field at the Fe probes in the octahedral site has a room temperature value of B_hf = 44.5(9) T. At higher sample temperatures, the B_hf becomes much weaker, with the Fe³⁺ hyperfine magnetic contribution disappearing above 700 K. Simultaneous analysis of the Ba–BFO eMS spectra shows that the variation of the hyperfine field with temperature follows the Brillouin curve for S = 5/2. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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10 pages, 1972 KiB

Open AccessArticle

Local Probing ErCrO₃

by Gonçalo N. P. Oliveira, Pedro R. Rodrigues, João G. Correia, João P. E. Araújo and Armandina M. L. Lopes

Crystals 2023, 13(1), 54; https://doi.org/10.3390/cryst13010054 - 28 Dec 2022

Cited by 5 | Viewed by 1992

Abstract

Local distortions in perovskite-like orthochromites are of extreme importance for the properties they exhibit. Here, we present the results of structural and DC magnetisation measurements combined with local probe studies in polycrystalline ErCrO₃. The electric field gradient (EFG) parameters’ evolution with [...] Read more.

Local distortions in perovskite-like orthochromites are of extreme importance for the properties they exhibit. Here, we present the results of structural and DC magnetisation measurements combined with local probe studies in polycrystalline ErCrO₃. The electric field gradient (EFG) parameters’ evolution with temperature shows two clear signals of local environment changes, one at the ferroelectric phase transition (T_FE) and the other below 250 K. At the claimed T_FE, the EFG changed from a slightly distorted axial symmetric to an EFG with axial symmetry (evidence that the local point-symmetry of the crystal might have changed). At a temperature around 250 K, we observed the development of a magnetic hyperfine field (MHF) and a change in the EFG to an axial slightly distorted one. These observations are rather in line with our magnetisation measurements, as a relatively strong coercive field was observed well above the Cr sub-lattice ordering temperature. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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13 pages, 3485 KiB

Open AccessArticle

Structure and Properties of Cubic PuH₂ and PuH₃: A Density Functional Theory Study

by Thomas Smith, Samuel Moxon, David J. Cooke, Lisa J. Gillie, Robert M. Harker, Mark T. Storr, Estelina Lora da Silva and Marco Molinari

Crystals 2022, 12(10), 1499; https://doi.org/10.3390/cryst12101499 - 21 Oct 2022

Cited by 3 | Viewed by 2443

Abstract

The presence of cubic PuH₂ and PuH₃, the products of hydrogen corrosion of Pu, during long-term storage is of concern because of the materials’ pyrophoricity and ability to catalyse the oxidation reaction of Pu to form PuO₂. Here, [...] Read more.

The presence of cubic PuH₂ and PuH₃, the products of hydrogen corrosion of Pu, during long-term storage is of concern because of the materials’ pyrophoricity and ability to catalyse the oxidation reaction of Pu to form PuO₂. Here, we modelled cubic PuH₂ and PuH₃ using Density Functional Theory (DFT) and assessed the performance of the PBEsol+U+SOC (0 ≤ U ≤ 7 eV) including van der Waals dispersion using the Grimme D3 method and the hybrid HSE06sol+SOC. We investigated the structural, magnetic and electronic properties of the cubic hydride phases. We considered spin–orbit coupling (SOC) and non-collinear magnetism to study ferromagnetic (FM), longitudinal and transverse antiferromagnetic (AFM) orders aligned in the <100>, <110> and <111> directions. The hybrid DFT confirmed that FM orders in the <110> and <111> directions were the most stable for cubic PuH₂ and PuH₃, respectively. For the standard DFT, the most stable magnetic order is dependent on the value of U used, with transitions in the magnetic order at higher U values (U > 5 eV) seen for both PuH₂ and PuH₃. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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15 pages, 525 KiB

Open AccessArticle

Local Crystalline Structure of Doped Semiconductor Oxides Characterized by Perturbed Angular Correlations: Experimental and Theoretical Insights

by Anastasia Burimova, Artur Wilson Carbonari, Nicole Pereira de Lima, Arnaldo Alves Miranda Filho, Alexandre Pinho dos Santos Souza, Tatiane da Silva Nascimento Sales, Wanderson Lobato Ferreira, Luciano Fabricio Dias Pereira, Bruno Santos Correa and Rajendra Narain Saxena

Crystals 2022, 12(9), 1204; https://doi.org/10.3390/cryst12091204 - 26 Aug 2022

Viewed by 1826

Abstract

Doping semiconductor oxides with trace amounts of non-native elements can improve their properties such as bandgap and conductivity. The lack of local techniques makes the precise characterization of these materials difficult. Among the few techniques capable of providing local characterization, those based on [...] Read more.

Doping semiconductor oxides with trace amounts of non-native elements can improve their properties such as bandgap and conductivity. The lack of local techniques makes the precise characterization of these materials difficult. Among the few techniques capable of providing local characterization, those based on hyperfine interactions at probe nuclei have the advantage of being well established, probing the material homogeneously and completely, thus investigating different regions of material. Some of these techniques are also quite sensitive even at extremely low dopant concentrations. The perturbed angular correlation technique, combined with first-principles calculations, has recently been shown to be a powerful method for characterizing doped semiconductor oxides. In this paper, we present a brief review of the unique information extracted from the semiconductor investigation with such a complex approach, including semiconductor oxides doped with cadmium and other elements. A strong relationship between the local environment, including electronic structure, and the nature of the dopant and the native element of the doped oxides is also shown. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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21 pages, 6310 KiB

Open AccessArticle

Diffusion of Tracer Atoms in Al₄Ba Phases Studied Using Perturbed Angular Correlation Spectroscopy

by Randal Newhouse, Samantha Cawthorne, Gary S. Collins and Matthew O. Zacate

Crystals 2022, 12(8), 1152; https://doi.org/10.3390/cryst12081152 - 16 Aug 2022

Cited by 1 | Viewed by 1680

Abstract

The Al₄Ba crystal structure is the most common structure among binary intermetallic compounds. It is well suited for accommodating large atoms of group II elements and is often the intermediate phase closest to the terminal phase. It is, therefore, of interest [...] Read more.

The Al₄Ba crystal structure is the most common structure among binary intermetallic compounds. It is well suited for accommodating large atoms of group II elements and is often the intermediate phase closest to the terminal phase. It is, therefore, of interest to characterize diffusion properties of compounds with this tetragonal crystal structure. In the present study, ¹¹¹In perturbed angular correlation spectroscopy was used to study solute site occupation and atom movement in In₄Ba, Al₄Ba, Al₄Eu, Al₄Sr, and Ga₄Sr. The indium tracer and its daughter cadmium were found to occupy only the two Al-type sublattices in these compounds through detection of nuclear quadrupole interactions with axially symmetric EFGs. Measurements with increasing temperature revealed merging of signals due to dynamical averaging of these interactions as Cd atoms jumped at increasing rates between alternating sublattices. The jump rates were estimated to be between 8 kHz and 2 MHz at about 350 °C for Al₄Eu and at about 450 °C for In₄Ba and Al₄Ba. Fits of spectra using Blume’s stochastic model allowed determination of activation enthalpies for average Cd jump rates between alternating Al sublattices in Al₄Sr and Ga₄Sr to be 1.16(3) eV and 1.47(3) eV, respectively. This result was used to estimate transverse diffusivities of Cd. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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15 pages, 1914 KiB

Open AccessEditor’s ChoiceArticle

Magnetic Structure and Strain State in Fe/V Superlattices Studied by ⁵⁷Fe⁺ Emission and Conversion Electron Mössbauer Spectroscopy

by Torben E. Mølholt, Sveinn Ólafsson, Haraldur P. Gunnlaugsson, Bingcui Qi, Karl Johnston, Roberto Mantovan, Hilary Masenda, Krish Bharuth-Ram, Hafliði P Gíslason, Guido Langouche and Deena Naidoo

Crystals 2022, 12(7), 961; https://doi.org/10.3390/cryst12070961 - 10 Jul 2022

Viewed by 1946

Abstract

The magnetic properties of the Fe/V superlattices were studied by conventional Conversion Electron Mössbauer Spectroscopy (CEMS) and online

^{57}

Fe

^{+}

emission Mössbauer Spectroscopy (eMS) at room temperature (RT) at ISOLDE/CERN. The unique depth-enhanced sensitivity and ultradiluted regime of the probe atoms adopted [...] Read more.

The magnetic properties of the Fe/V superlattices were studied by conventional Conversion Electron Mössbauer Spectroscopy (CEMS) and online

^{57}

Fe

^{+}

emission Mössbauer Spectroscopy (eMS) at room temperature (RT) at ISOLDE/CERN. The unique depth-enhanced sensitivity and ultradiluted regime of the probe atoms adopted in this eMS facility enabled the investigation of the magnetic structures and the strain state in the superlattice layers and at the interfaces. The magnetic spectra of the superlattices were found to depend on both the local lattice environment and the strain state of the Fe-lattices. The magnetic polarisation in the V-layers or at the interfaces was not detected at RT. Spectral broadening was evident in the single line component of the eMS due to Fe ions substituted at V-lattice sites in the V-layers of the superlattice, attributable to the lattice strain in the V-layers. Our study demonstrate that with the online eMS technique the effects of the strain state of the superlattice on the magnetic properties of the Fe-layer in the Fe/V multilayer structures can be detected. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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11 pages, 5605 KiB

Open AccessArticle

Introducing Ultra-Low Energy Ion Implantation of Radioactive Isotopes at ISOLDE, CERN for (Near-)Surface Characterization: The ASPIC and ASCII Vacuum Chambers

by Koen van Stiphout, Leonard-Alexander Lieske, Manuel Auge and Hans Hofsäss

Crystals 2022, 12(5), 626; https://doi.org/10.3390/cryst12050626 - 27 Apr 2022

Cited by 1 | Viewed by 2307

Abstract

Solid-state physics research has long employed radioactive isotopes to investigate the crystallographic, electric and magnetic properties of nanostructures. Ion implantation (1–100 keV) is the method of choice for incorporating radioactive nuclei into the crystal structure. However, the enormous scientific interest in 2D materials, [...] Read more.

Solid-state physics research has long employed radioactive isotopes to investigate the crystallographic, electric and magnetic properties of nanostructures. Ion implantation (1–100 keV) is the method of choice for incorporating radioactive nuclei into the crystal structure. However, the enormous scientific interest in 2D materials, multiferroics and their interfaces of the last decades has lead to more stringent demands for isotope incorporation. Ultra-low energy (ULE) ion implantation (10–100 eV) provides the ability to precisely tune the depth of the implanted radioactive probes, even in the case of atomically thin 2D materials. To unlock this potential and expand the experimental capabilities of the ISOLDE collaboration in CERN, the apparatus for surface physics and interfaces at CERN (ASPIC), an experienced ultra-high vacuum chamber dedicated to surface characterization and modification, is refurbished and upgraded with a new component: the ASPIC’s ion implantation (ASCII) chamber, designed for ULE ion implantation of radioactive probes. This paper describes the scientific context, design and application of these vacuum chambers. Full article

(This article belongs to the Special Issue Radioactive Isotopes Based Materials Characterization)

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