Surface structure of In3Ni2 Inter-metallic compound
Inter-metallic compounds can be used as catalysts as they show better selectivity and superior long-term stability for specific catalytic reactions compared to their elemental counterparts [1]. In3Ni2 acts as catalyst for hydrogenation of carbon dioxide into methanol [2]. Understanding of surface structure and electronic properties of In3Ni2 would help to learn and optimise the catalytical activities.This work describes the first study of atomic structure of In3Ni2 by two surface science techniques, Scanning Tunnelling Microscopy (STM) and Low Energy Electron Diffraction (LEED). All high symmetry surfaces (100), (001) and (2¯10) prepared by sputtering (Ar+ for 30 minutes, drain current 5-6 µA) and annealing at 350-550 oC.
We found that surface ordering starts at annealing temperature of 350 oC and high-quality LEED patterns are observed at 480 oC.
LEED patterns for two surfaces (100) and (001) reveal bulk truncated surface, (1×1) structure. However, surface (2 10) has (2×1) structure. Atomic resolution is obtained in STM images, which can be explained using the model atomic structure. Furthermore, the (001) surface shows a c-(2√3 × 4) rectangular superstructure with three domains that formed from deposit H2-deposition, which is confirmed by both LEED and STM.
References:
[1] M. Ivanov, V. Berezutskii, M. Shevchenko, V. Kudin, and V. Sudavtsova, Powder Metallurgy and Metal Ceramics, vol. 54, no. 7, pp. 465–470, 2015
[2] C. Li, Y. Chen, S. Zhang, S. Xu, J. Zhou, F. Wang, M. Wei, D. G. Evans, and X. Duan, Chemistry of Materials, vol. 25, no. 19, pp. 3888–3896, 2013
Superconductivity and possible variable range hopping in (TiZrNbCu)1-xNix, (TiZrNbNi)1-xCux and (TiZrNbCu)1-xCox complex amorphous alloys
We present the result of a systematic study of electrical resistivity, superconductive transitions and Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals in a broad composition range x (0.1-0.5). All samples showed a high resistivity at room temperature (140-240 µΩ cm) and the superconducting transition temperatures decrease with increasing TL content, similar to binary amorphous [3] and crystalline HEA TE-TL alloys [4]. With the highest recorded transition for (TiZrNbCu)0.90Co0.10 at 1.94 K. The Hall coefficient RH is temperature independent and positive for all samples except for (TiZrNbCu)0.57Co0.43 with an interpolated critical concentration at xc=0.34, in good agreement with binary TE-TL alloys [1]. For the temperature dependence of resistivity, we discuss possible variable range hopping (VRH) like parallel conduction mode, in temperature range 30-150K, with an exponent p=1/2. We examine this in the context of VRH in granular materials [2].References:
[1] J. Ivkov and E. Babić, J. Phys.: Condens. Matter 2 (1990) 3891
[2] V. F. Gantmakher, Electrons and Disorder in Solids (OUP Oxford, 2005)
[3] E. Babić et al, Solid State Commun. 39 (1981) 139
[4] K. Stolze et al, Chem. Mater. 30 (2018) 906
Multiscale quasiperiodic metallic alloys and characterising their physical properties
Quasicrystals (QC) are complex metallic alloys with long-range crystallographic order and aperiodicity, leading to a unique combination of properties [1]. The structure of most common QCs has been understood and various novel structures have been observed in thin films on QC surfaces [2,3]. Quasiperiodic tilings are models which describe the atomic surface structure of QC; molecular overlayers have been shown to selectively absorb on QC surfaces forming such tilings [2]. However, characterising the physical properties of these atomic-scale QC structures is challenging due to various limitations associated with UHV experiments.The presenting research overcomes limitations by fabricating mesoscopic 2D quasiperiodic tilings of metallic alloys with thermal nanolithography. The aim of fabricating tilings with nanolithography is to understand the magnetic properties of tilings, in relation to QC structure. Amman-Beenker, Penrose, and Fibonacci tilings have been fabricated, among others, with magnetic Ni_4Fe decorating the tilings and imaged with electron microscopy. These tilings model the surface of 8-fold, 5-fold, and 2-fold complex metallic alloys. In future, the tilings will be imaged with magnetic microscopy methods.
References:
[1] D. Shechtman and I. A. Blech. Metallurgical Transactions A, vol. 16, no. 6, pp. 1005–1012, 1985
[2] S. Coates, et al. Nature communications, vol. 9, no. 1, pp.1–5, 2018
[3] V. Fournée, et al. Recent Advances in Thin Films, pp. 13–34, Springer, 2020
From simple to complex structures one step at a time: calcium-containing nitridochromates
Exploratory research on calcium-containing nitridochromates with incorporation of lithium and fluoride resulted in a plethora of new compounds, crystallizing in often unique crystal structures. The complexity of the structures increases from simple 3:1:3 composition in Ca3[CrIIIN3][1] to nitridochromates with mixed anions, as well as cations. Different cationic and anionic species influenced the oxidation state of chromium and resulted in phases with Cr(III) and the otherwise mostly elusive Cr(IV). The compounds will be discussed with regards to corresponding prototype structures, as well as other known nitridochromates.
[1] Höhn, P. and R. Niewa, Handbook of Solid State Chemistry. 2017, Wiley-VCH. p. 251-359
Truly colossal negative magnetoresistance in EuCd2As2 at low temperatures
Weyl semimetals have attracted much attention due to their wide range of exotic properties predicted in theories. They represent an elegant example of the correspondence between condensed matter and high-energy physics because of its low-energy excitations. The Weyl fermions are massless particles (which obey the Weyl equation). Their energy bands show linear dispersion in the vicinity of nodes, termed the Dirac or Weyl points, as the three-dimensional analogue of graphene. The high mobility of charged Weyl fermions may find use in electronics and computing.Layered antiferromagnet EuCd2As2 was predicted to be a Weyl semimetal. We shall present electrical transport and magnetic properties of a single crystal of EuCd2As2 with insulating behaviour. The samples exhibit VRH transport regime with colossal negative magnetoresistance of five orders of magnitude. Our findings cast a different light on previously reported interpretations of physics in EuCd2As2.
Nb-Ni binary compounds in oxygen evolution reaction
Hydrogen generation through electrochemical water splitting offers a sustainable and fossil-free solution for high quality hydrogen production. The oxygen evolution reaction (OER) is kinetically challenging due to complex processes with multielectron transfer comparing to hydrogen evolution reaction [1]. The feasibility of water electrolysis on large industrial scale is subject to develop highly effcient, stable, viable, and low-cost electrocatalysts for OER half-reaction. Recent studies have shown that transition metal catalysts (Ni, Co and Fe, etc.) as well as their compounds such as borides, carbides, nitrides and oxides, possess high OER activity and reasonable stability in alkaline environment aside from their relative low cost [2].In our work, electrochemical behavior of Nb-Ni binary compounds in terms of their OER activity was investigated. Binary compounds NbNi3 and Nb7Ni6 were synthesized via arc melting followed by homogenization annealing. The results of electrochemical studies in alkaline electrolyte, supported by extensive characterization of electrode material before and after electrochemical experiments, will be presented.
References:
[1] N. T. Suen et al., Chem. Soc. Rev. 2017, 46, 337
[2] L. Sun et al., Coord. Chem. Rev. 2021, 444, 214049
High-fluence ion irradiation for materials testing
Energetic ion beams are commonly utilized to modify the properties and study accelerated radiation ageing of materials. In this contribution, we present our research on the application of high-energy ion irradiation as a surrogate for neutron radiation in nuclear reactors and experimental simulation of radiation conditions in Space. The ion beam laboratory of the Slovak University of Technology in Bratislava provides ion beams with energies up to 100 MeV. High fluence irradiations aim to investigate the effect of radiation environments on various materials from atomic-scale, particularly defect evolution, void and bubble formation followed by aggregation, transmutation – up to the macroscale, i.e. impact on engineering relevant properties. While the nanoscale defects are being probed by non-destructive analytical techniques such as positron annihilation spectroscopy, the macroscale properties by micro-mechanical testing techniques. The latest results on the effect of transmutation helium on the Eurofer97 steel and its Oxide Dispersion Strengthened variant are presented along with the capabilities of the laboratory.Photoresponse behavior of Dye Sensitized Solar Cells
The work reports about the behaviour of Dye Sensitized Solar cells. When exposed to 1.5 AM solar radiation generated by a solar simulator, the open circuit voltage (Voc) of the fabricated cells was measured as a function of time (for 30 days). The solar cell was fabricated using combination of three electrodes (one indium tin oxide (ITO) and two aluminium doped zinc oxide (AZO) under different conditions), two electrolytes (potassium iodide (KI) and lithium iodide (LiI)) and two dyes (Eosin Yellow and Ruthenium Red). A total of 12 solar cells were prepared using different combination of electrolyte, dye and electrodes. A variety of structural and elemental analyses were performed. XRD and Raman spectroscopy are used to characterize the deposited films and confirm the deposition of AZO films. The thickness and surface morphology of the films were measured using SEM. Elemental analysis was performed using EDX. Transparency of the film has been studied by US Vis spectrometry. Current-Voltage characteristic has also been studied with an aid of 4-point probe method. It was observed that AZO electrode with KI-EY and KI-Ru combination showed better results than the ITO electrode.This work is in part supported by the scientific project „Intercalated transition metal dichalcogenides“ (HrZZ IP-2020-02-9666).
Characterization of Ga-Ni-Co-Cr-Fe-based multi-principal element alloys
The effect of changes in gallium and nickel content on the microstructure and properties of (GaNi)xCoCrFe (x = 0.4, 0.7, 1.0, 1.3 and 1.6) multi-principal element alloys was investigated. The (GaNi)0.4CoCrFe alloy contains an FCC phase and when the ratio of gallium and nickel increases at the expense of the rest of the elements, a gradual change from FCC to BCC is observed. The hardness of alloys correlates with their phase composition. The density of the alloys gradually decreases as the ratio of gallium and nickel increases due to the low density of gallium. Some preliminary results of mechanical testing will also be presented.We acknowledge financial support from Slovak grants APVV-20-0124 and VEGA 1/0692/22, as well as the European Regional Development Fund, project No. ITMS2014+: 313011W085.
Phase transformation in decagonal Al-Cu-Rh quasicrystals induced by phasons
We will present the results of the refinement of the decagonal Al-Cu-Rh quasicrystal structure model based on high-temperature data [1] using a new phason approach [2,3] and a generalized Penrose tiling (GPT) as a quasilattice [4]. A correlation between lattice parameters and the maximal residual electron density was observed, indicating a phase transformation at a temperature around 1083-1153 K. Phasonic disorder is modeled as a distribution of moments. Minima of values of moments are observed at 1083-1153 K, too, leading to the conclusion that the transition to a more stable phase is related to phason disorder.The occurrence of the additional 5th atomic surface in GPT can be obtained by phasonic fluctuation of the ideal structure. In the refinement, we observed that the atomic distribution of the 5th atomic surface correlates with the stability of a structure at the temperature of approximately 1153 K, which could indicate the influence of the phason disorder on the stabilization of the structure [5].
References:
[1] P. Kuczera, J. Wolny, W. Steurer, Acta Cryst. B 70 (2014) 306
[2] I. Bugański, R. Strzałka, J. Wolny, Acta Cryst. A 75 (2019) 352
[3] I. Bugański, R. Strzałka, J. Wolny, J. Appl. Cryst. 53 (2020) 904
[4] M. Chodyn, P. Kuczera, J. Wolny, Acta Cryst. A 71 (2015) 161
[5] I. Bugański, R. Strzałka, J. Wolny, Acta Cryst. A A 78 (2022) 402
Emergence of intercalated transition metal derived bands near the Fermi level of (Co, Ni)1/3NbS2
Transition metal intercalated NbS2 have been studied for decades, yet their complexities remain to be solved. The host 2H-NbS2 is a superconductor below 6 K. Intercalation of transition metal atoms suppresses the superconductivity and introduces magnetic ordering. A series of 3d transition metal intercalated NbS2 forms in a certain concentration M1/3NbS2 (M: 3d transition metal), and their magnetic structure depends on a selection of transition metals. Both Co1/3NbS2 and Ni1/3NbS2 exhibit antiferromagnetic ordering in ab-planes at TN ∼ 26 and 90 K, respectively. We performed angle-resolved photoelectron spectroscopy on Co1/3NbS2; and Ni1/3NbS2 to study their electronic structure. The observed band dispersion of both compounds showed the similar features as 2H-NbS2 bands. However, a clear distinction from 2H-NbS2 bands was observed in the vicinity of the Fermi level as a shallow electron pocket originating from the intercalated atoms.This work is in part supported by the scientific project "Pressure- and Temperature-driven Phase transitions in Strongly Correlated Electron Systems" (PaT PiSCES, HrZZ UIP-2019-04-2154)
Synthesis and characterization of magnetic transition metal chalcogenides
Two dimensional magnetic materials have been gaining attention as potential candidates for spintronic devices. Among them, transition metal dichalcogenides intercalated by magnetic atoms have been intensively studied due to their structural diversity, and rich electrical and magnetic behaviors. One of the most interesting series of materials is MxNbS2 (M: 3d transition metal). Intercalated ions occupy octahedral vacancy sites in the van der Waals gaps and form super-lattice structures. We have grown Co1/3NbS2 and Ni1/3NbS2 single crystals by chemical vapor transport method using iodine as a transport agent. The grown crystals have been characterized by powder x-ray diffraction, magnetic and electrical transport measurements. Both crystals formed into a hexagonal structure (space group: P6322). Co1/3NbS2 and Ni1/3NbS2 showed antiferromagnetic ordering at TN~25 and 91 K, respectively, that were in good agreement with previous studies [1, 2]. Details of the synthesis and analysis will be discussed in the poster presentation together with our latest progress in the growth of transition metal phosphides samples (Mn2P, MnP and Fe2P).This work is in part supported by the scientific project „Intercalated transition metal dichalcogenides“ (HrZZ IP-2020-02-9666).
References:
[1] P. Popčević et al., Physical Review B 105, 155114 (2022)
[2] R. H. Friend et al., Philos. Mag. 35, 1269 (1977)
Contributions to the understanding of thermal and electronic transport in complex metallic compounds: from periodic to quasi-periodic crystals
Building on the expertise of the investigation (measuring, analyzing and interpreting) of thermal and electrical transport in the field of strongly anisotropic inoraganic quasi-onedimensional periodic systems [1-3], with our collaborators at CRTB in Grenoble we expanded our interest to investigation of the transport and magnetic properties of quasiperiodic systems [4, 5]. In cooperation with the NMR group of professor J. Dolinšek (IJS, Ljubljana, SLO) we have intensified, the initiated research of quasiperiodic systems, within the framework of bilateral CRO-SLO cooperation. The collaboration was very motivating and fruitful, both educationally and scientifically. It resulted with successful completion of several doctoral theses on both sides. The results of this collaborative complementary research have been presented at numerous conferences, workshops and schools organized within as well as wider than the framework of EU cooperation: first the EU project Complex metallic alloys (CMA) and then within the EU network C-MAC (today ECMetAC).On the occasion Prof. J. Dolinšek's 65th birthday, we will present some highlights of our contributions to the understanding of quasi-periodic systems, presented in ref. [6-12].
This work is in part supported by the scientific project „Intercalated transition metal dichalcogenides“ (HrZZ IP-2020-02-9666).
References:
[1] A. Smontara, et.al, J. of Phys.: Cond. Matter 4 (1992) 3273
[2] A. Smontara, et. al., Phys. Rev. B 48 (1993) 4329
[3] A.Smontara, et. al., Phys. Rev. Lett. 77 (1996) 5397
[4] A. Bilušić, et.al., Mat. Sci. Eng. A, 294 (2000) 711
[5] A. Bilušić, et.al, Vacuum 61 (2001) 345
[6] A. Bilušić, et.al., J. Alloys and Comp 342 (2002) 413
[7] J. Dolinšek, et al., Phys. Rev. B 72 (2005) 064208
[8] Ž. Bihar, et.al., J. Alloys and Comp 407 (2006) 65
[9] A. Smontara, et.al, Phys. Rev. B 78 (2008) 104204
[10] P. Popčević, et al., Phys. Rev. B 81 (2010) 184203
[11] M. Bobnar, et.al. Phys. Rev. B 85 (2012) 024205
[12] P.Popčević, et. al., in preparation
Tuning thermal conductivity of hydrogen fuel cell catalyst films
Catalyst films (polymer electrolyte membranes) are prepared at Faculty of Science, University of Split and successfully implemented into hydrogen micro fuel cells with promising performance. Catalyst films are to be modified by addition of noble metal-based multimetallic nanoparticles with the aim of increasing dry film electron conductivity, proton and lateral heat conductivity thus improving fuel cell efficiency and longevity.We present the experimental setup for automating high temperature electrical and thermal measurement in arbitrary atmosphere (Argon, vacuum). 3? measurement technique is chosen for thermal measurements and can be applied to bulk amorphous solids, crystals and amorphous films tens of microns thick [1]. Micro heaters are fabricated by photolithography onto a measured material. AC current is passed through the micro heater with frequency ?, which induces local heating of the material as a function of 2?. Resistance depends linearly on the temperature change. Voltage differential across the metallic heater is measured. The third harmonic of the voltage differential contains information on the thermal properties of the material. Electrical and thermal measurements are automated through software (LabVIEW).
Reference:
[1] David G. Cahill, Review of Scientific Instruments 61, 802 (1990)
Influence of surface oxidation on the OER activity and stability of ZrNi and ZrCo
Hydrogen production by mean of water electrolysis is a promising strategy to efficiently store energy from intermittent renewable power sources. The oxygen evolution reaction (OER) occurring at the anode is kinetically slow and reduce the overall efficiency of current electrolyzers. The discovery of new anode material possessing enhanced OER activity is therefore of tremendous importance nowadays. In addition, the electrode material must also show high operating stability to withstand the harsh industrial conditions which involve high current densities, highly concentrated alkaline electrolyte and elevated temperatures [1].In our approach a controlled oxidation of bulk intermetallics material to form a thin oxide layer at the surface was carried out. In this way, the formation of a catalytically active oxide layer, that will at the same time protect the conductive intermetallic underneath and preserve sufficient electrical conductivity of the electrode was attempted. The present contribution will focus on the results obtained by applying this approach to the rare-metal free ZrNi and ZrCo compounds. The OER activity and the stability over time of electrodes which have been treated under different oxidation conditions will be compared and discussed.
Reference:
[1] M. Chatenet et al., Chem. Soc. Rev. (2022) 51, 4583