Electronic and magnetic properties of Tb₂FeCrO₆(TFCO) is investigated using density functional theory (DFT). TFCO shows the insulating property with band gap of 0.048 eV and 2.372 eV within generalized gradient approximation (GGA) and GGA+U respectively. The anti-ferromagnetic configuration, AFM2
[FeFeCrCr- ↑↓↑↓ ] is found to be ground state. Further, exchange coupling interactions are calculated to get depth knowledge on the magnetic realm of
TBCO.

In this work we have investigated electronic, magnetic and transport properties of rare-earth ternary compound BaTbO₃ based on density functional theory using the generalized gradient approximation. This material is found to be ground state antiferromagnetic semiconducting in nature with direct energy gap of 0.8 eV. The study of transport properties under constant relaxation time approximation (τ=10^-14) and rigid band approximation using BoltzTraP code in the temperature range 300-1200 K have found large value power factor and figure of merit 124 µW cm^-1K^-2 and 0.78 respectively at 1200 K, and can be enhanced with p-type dpoing. Which indicates the potential candidate for good thermoelectric material.

Weyl semimetals are the novel topological class of materials having huge applications on quantum computing and spintronics devices. These materials are believed to be the host of the massless but charged quasi particles called Weyl fermions. The Weyl semimetallic phase arise in the crystals when the two non degenerate valance and conduction band touch or cross nearby the Fermi level creating a node called as Weyl node. Here we focus on studying the first principle calculation of the electronic, magnetic and topological properties of the layered material Fe₂Sn and Fe₃Sn using Full Potential Local Orbital Code (FPLO). From our density functional theory calculations, the magnetic ground state is found to be ferromagnetic with a total magnetic moment of 9.12μ_B/unit cell and 14.09 μ_B/unit cell of Fe₂Sn and Fe₃Sn respectively. The electronic state of both shows metallic behavior with the band crossing close to the Fermi level. The systems are predicted to be magnetic WSMs based on the identification of Weyl points close to the Fermi level with chirality 1 or -1. Moreover, the high peak values of anomalous hall conductivity are observed in the energy range of Weyl points.

Thermotropic ionic liquid crystals are considered very promising functional electrolytes in DSSCs, batteries, fuel cells and capacitors^1,2 for their unique combination of anisotropic ion conductivity and high polarizability.³ Moreover, they are interesting in the optoelectronic field as electrooptical functional unit.^3-5 Many efforts have been devoted to the design of liquid crystals salts based on the viologen unit as organic cation, due to their interesting electrochromic and electrochemical properties.⁶ Most of the reported structures contain flexible chains directly linked to the nitrogens of the bipyridine rings.⁶ Their thermotropic behavior depends on the nature of the anion and of the N-substituents. A suitable choice of the latter makes access to different molecular orbital energy levels allowing different colors of the corresponding radical cation. N-Aryl substituted viologens, are of great interest because they show green colored radical cations due to the delocalization of the radical-cation over an extended p-system.⁷. Herein, we present a series of new N-aryl substituted liquid-crystalline viologens based on mono(4-alkylphenyl) and bis(4-alkylphenyl) bipyridinium cations with the same counterion but different alkyl chains (n=8, 10,12, 14), reporting their thermal behavior, their mesomorphic properties as a function of the chain length and their electrochromic properties in solution and in the LC phase.⁷

References:

[1] Pan, X.; Wang, M.; Fang, X.Q.; Zhang, C.N.; Huo, Z.P.; Dai, S.Y.; Sci. China: Chem., 2013, 56, 1463–1469.

[2] Sasi, R.; Chandrasekhar, B.; Kalaiselvi, N.; Devaki, S.J.; Adv. Sustainable Syst., 2017, 1, 1600031.

[3] Axenov, K.V., Laschat, S.; Materials, 2011, 4, 206.

[4] Bhowmik, P.K.; Kareem, M.; Al-Karawi, M.K.M.; Killarney S.T.; Dizon, E.J.; Chang, A.; Kim, J.; Chen, S.L.; Principe, R.C.G.; Ho, A.; Han, H.; Mandal, H.D.; Cortez, R.G.; Gutierrez, B.; Mendez, K.; Sharpnack, L.; Agra-Kooijman, D. M.; Fisch, M.R.; Kumar, S.; Molecules 2020, 25(10), 2435.

[5] K. Goossen, K. Lava, C. W. Bielewski, K. Binnemans, Chem. Rev., 2016, 116, 4643.

[6] Monk, P.M.S., The viologens: physico-chemical properties, synthesis and application of the salt of 4,40-bipyridine, John Wiley and Sons, Inc., Wiley – VCH, New York, Weinheim, 1998.

[7] Veltri, L.; Cavallo, G.; Beneduci, A.; Metrangolo, P.; Corrente, G.A.; Ursini, M.; Romeo, R.; Terraneo, G.; Gabriele, B.; New J. Chem., 2019, 43, 18285-18293.

Binary copper oxides [Cu-O] are enjoying large attention from a broad scientific community due to their electronic and optical properties that render them promising candidates for photovoltaics and for all-oxide electronics. They are excellent light absorbers across the visible energy range, exhibit excellent stability, are non-toxic and simply manufactured. Furthermore, they give rise to a vast family of semiconductors and superconductors, and as such belong to the most studied transition metal oxides [1,2]. Interestingly, only three binary phases are known Cu₂O, Cu^IIO and Cu^I₂Cu^II₂O₃ although there are many indications scattered across the known literature that suggest formation of various other stoichiometries [3,4]. Also, no binary oxide with Cu^III is known even though it is perfectly valid oxidation state of copper. The recognized technological potential of copper oxides as well as our chemical curiosity urges us for their immediate exploration. In this contribution we provide new theoretical evidence for phase diversity among the binary copper oxides by addressing the ‘suspected’ stoichiometries and oxidation states with various Density Functional Theory approaches. We take advantage of the structural diversity observed in the binary and ternary transition metal oxides and evaluate accessibility of their crystal structures to various copper oxidation states, electronic configurations (high-spin, low-spin), ionic sizes and shapes in hypothetical binary copper oxides obtained by M --> Cu substitution. We will present details of calculated crystal, electronic and magnetic structure and vibrational spectra for the most interesting cases.

Acknowledgement: The European Regional Development Fund, Research and Innovation Operational Programme, for project No. ITMS2014+: 313011W085; Scientific Grant Agency of the Slovak Republic, grant No. VG 1/0223/19; the Slovak Research and Development Agency, grant No. APVV-18-0168; Aurel supercomputing infrastructure in CC of Slovak Academy of Sciences acquired in projects ITMS 26230120002 and 26210120002 funded by ERDF.

References:

[1] B. K. Meyer et al., Phys. Status Solidi B, 249, 8, 1487 (2012).

[2] T. K. S. Wong, S. Zhuk, S. Masudy-Panah, G. K. Dalapati, Materials, 9, 271 (2016).

[3] D.L. Cockea et al., Vacuum, 79, 71 (2005).

[4] G.K. Moiseev and A.L. Ivanovskii, Neorganicheskie Materialy, 42, 700 (2006).

The control of the particle size distribution, crystal habit, and crystal purity is crucial in most crystallization processes to meet the targeted critical quality attributes of the final product. Over the last two decades, several model-free strategies, such as supersaturation control and direct nucleation control, and model-based techniques, such as model predictive control, have been developed and implemented in a wide range of scientific and industrial sectors, particularly the pharmaceutical industry. Despite the significant progress, there is still an increasing demand for more advanced, versatile, robust, and cost-effective optimization and control technologies for both batch and continuous crystallization processes to ensure, through real-time trajectory tracking control, high product quality and reduce batch-to-batch variation and wastes. A novel optimal trajectory tracking control strategies of a batch cooling crystallization processes based on reinforcement learning is presented. The cooling crystallization of paracetamol in water was used as a case study. A model-based technique is implemented, using a dynamic mathematical model validated elsewhere, to reduce the experimental burden and explore wider design and operating spaces. The main objective is to achieve a large crystal size and reduce the deviation from a targeted final yield and coefficient of variation. Several training strategies and reward functions were tested to help achieve robust optimal training of the agent. The agents, with the best training features, were validated against different particle size, temperature, and supersaturation trajectories, then compared to benchmark control techniques, such as supersaturation control and model predictive control.

Non-stoichiometric hydroxyapatite (HAP, Ca10(PO4)6(OH)2) and whitlockite (β-TCP, β-Ca3(PO4)2) enter the human mineral mass. For this reason, phases with a structure of apatite and whitlockite are widely used as biocompatible materials both for the diagnosis of various diseases and for the bone tissue implants.

Many researchers modify the properties of calcium phosphates by introducing various divalent and rare-earth substitution cations [1,2,3,4].

The introduction of rare-earth elements into the crystal lattice has become a very relevant research area for the development of new hybrid materials for sensing, biomedical imaging, drug delivery, etc [5].

Although doped phases based on tricalcium phosphate are actively studied as biomaterials, there is still no reliable data on the influence of the atomic position and distribution of cations on the biological properties of these phases. For this reason, an important task in the study of whitlockite-like (β-TCP) minerals and apatite is their investigation through a multi-methodological approach based on powder X-ray diffraction [6], photoluminescence, Raman and Fourier Transform Infrared (FTIR) spectroscopy, to reveal the various substitutions and understand the onset of properties, especially bioactive ones.

The structural aspects of some whitlockite and hydroxyapatite compounds, doped with different rare-earth cations, will be discussed along with the examination of the occupancies to clarify the location of the respective dopant. This information turn out extremely useful for a physico-chemical characterization aimed at understanding the properties and simulate the biological activity.

References

1. Kannan, S. Pina, J.M.F. Ferreira, Formation of strontium-stabilized β-tricalcium phosphate from calcium deficient apatite, J. Am. Ceram. Soc. 89 (2006) 3277–3280.
2. Mellier, F. Fayon, V. Schnitzler, P. Deniard, M. Allix, S. Quillard, D. Massiot, J.-M. Bouler, B. Bujoli, P. Janvier, Characterization and properties of novel gallium doped calcium phosphate ceramics, Inorg. Chem. 50 (2011) 8252–8260.
3. Quillard, M. Paris, P. Deniard, R. Gildenhaar, G. Berger, L. Obadia, J.-M. Bouler, Structural and spectroscopic characterization of a series of potassium- and/or sodium-substituted β-tricalcium phosphate, Acta Biomater. 7 (2011) 1844–1852.
4. V. Fadeeva, М. R. GafurovГафуров, Ya. Y. Filippov, G. А. DavydovaДавыдова, I. V. Savitzeva, А. S. Fomin, N. V. Petrakova, О. S. Antonova, L. I. Ahmetov, at. all. B. Copper-substituted tricalcium phosphates. Academy of Sciences reports, 2016, 471, p. 1–4.
5. Comby, E.M. Surender, O. Kotova, L.K. Truman, J.K. Molloy, T. Gunnlaugsson, Lanthanide-functionalized nanoparticles as MRI and luminescent probes for sensing and/or imaging applications, Inorg. Chem. 53 (2014) 1867–1879.
6. Altomare, C. Cuocci, C. Giacovazzo, A. Moliterni, R. Rizzi, N. Corriero, A. Falcicchio. J. Appl. Cryst. 2013, 46, 1231.

LiNbO₃ single crystals were first grown more than 50 years ago. Since that time thousands of papers have been published dealing with their outstanding ferroelectric, acoustic, nonlinear optical, holographic etc. properties and demonstrating their countless realized or potential applications. It was about 25 years ago, when the first stoichiometric LiNbO₃ crystals gave a new impulse to the never-ending investigations. Different applications require different undoped or doped systems of bulk, thin film, or nanocrystal forms. In the present talk I’ll show two examples, (i) incorporation of dopants into stoichiometric crystals, and (ii) properties of LiNbO₃ nanocrystals prepared by high-energy ball-milling.

Dopants are generally used to tailor the crystal properties for a given application. To understand the effect of dopants the incorporation mechanism and/or the substitution site in the crystal have to be known. Our IR absorption studies unambiguously showed that for the di-, tri-, and tetravalent cations a threshold concentration exists above which the dopants partially substitute at Nb sites, while below it they can be found on Li sites [1].

Nano-crystalline LiNbO₃ was prepared from single crystals by the high-energy ball-milling technique [2]. During milling the material suffered partial reduction that lead to the formation of bipolarons and polarons yielding gray color together with Li₂O segregation on the open surfaces. Upon high temperature oxidation, the volatile Li₂O phase and the polarons got eliminated and a more stable LiNb₃O₈ shell was formed. The particle size of the nano-crystals were determined by dynamic light scattering (DLS) and scanning electron microscopic (SEM) methods.

This research was supported by the National Research, Development and Innovation Fund of Hungary within the Quantum Technology National Excellence Program (Project No. 2017-1.2.1-NKP-2017-00001)

[1] L. Kovács, L. Kocsor, É. Tichy-Rács, K. Lengyel, L. Bencs, G. Corradi, Opt. Mat. Express 9, 4506 (2019).

[2] L. Kocsor, L. Péter, G. Corradi, Z. Kis, J. Gubicza, L. Kovács, Crystals 9, 334 (2019).

Rb₂Ni₃S₄ is a Kagome system belonging to the space group Fmmm (Orthorhombic). Here we performed density functional theory (DFT) calculation using the full potential local orbital code (FPLO) and identified ferromagnetic ground state with low magnetic moment. We consider Co doping by replacement of Ni on Rb₂Ni₃S₄ . Interestingly half metallic ferromagnetic behavior is observed with a total magnetic moment of 1.999 µ_B / unit cell. This indicates that the material is suitable spintronics device application in Kagome system. Moreover, due to the strong localization of electrons the flat band is observed near the vicinity of Fermi level which would be supportive in the study of possible super conducting nature of the material.

With the presence of robust flat band in YCo₅ which has high Magnetocrystalline Anisotropy Energy (MAE) among itinerant magnets, doping of hole to the Y-site with smaller ionic radii has shown significant change in the MAE. This system is found to be pseudo two dimensional ferromagnetic in nature under density functional calculations employing GGA+U exchange potential in WIEN2k. With hole doping the original flat band is extended to whole Brillouin zone. In addition to it the Fermi level is shifted because of it. The exchange interaction is evaluated for pristine and doped system using Heisenberg Hamiltonian and the Curie temperature evaluated was close to the experimental results. This enables to control the filling of flat bands upon doping, resulting in novel feature of band engineering.