LABORATORY FOR SYNTHESIS and CRYSTALLOGRAPHY OF FUNCTIONAL MATERIALS
12/2020
Merry Christmas and Happy New 2021!
Never have we ever been so thankful that a year passed, as in the case of 2020 :-)
12/2020
Our laboratory received the RBI Annual Award!
11/2020
It is quite cold but we do not surrender - science has to go forward :-)
Blast from the past
June, 2017
Yamadera (山寺) is a scenic temple located in the mountains northeast of Yamagata City, Tohoku Perfecture. Japan. The temple grounds extend high up a steep mountainside, from where there are great views down onto the valley.
Having the greatest time in mountains while taking the break from the experiments at Tohoku University, Sendai.
07/2020
Farewell party for our Sanja who is going to postdoc in Prague!
Sanja is going for one-year postdoc at Charles University in Prague in group of Prof. Milan Dopita at Faculty of Mathematics and Physics
05/2020
Our new paper in Inorganic Chemistry is out!
A molecule-based ferroelectric triethylmethylammonium tetrachloroferrate(III) ([N(C2H5)3CH3][FeCl4]) powder was designed as a multifunctional material exhibiting excellent multiple bistability. Prepared by the slow evaporation method at room temperature, the compound crystallizes in the non-centrosymmetric assembly of hexagonal symmetry (P63mc space group) which undergoes a reversible temperature-triggered phase transition pinpointed at 363 K to the centrosymmetric packing within the P63/mmc space group. Aside from the inseparable role of the symmetry-breaking process smoothly unveiled from the X-ray powder diffraction data, a striking change in the dielectric permittivity observed during the paraelectric-to-ferroelectric phase transition directly discloses the bistable dielectric behavior—an exceptionally high increase in the dielectric permittivity of about 360% at 100 kHz across the heating and cooling cycles is direct proof showing the highly desirable stimuli-responsive electric ordering in this improper ferroelectric architecture. Due to the magnetically modulated physical properties resulting in the coupling of magnetic and electric orderings, the flexible assembly of [N(C2H5)3CH3][FeCl4] could be used to boost the design and development of novel magnetoelectric devices.
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https://www.irb.hr/Novosti/Razvijen-novi-hibridni-molekulski-multiferiok
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05/2020
Due to COVID-19 we are still in, but our first paper about spacer cation engineering for achievement of phase control in J. Mater. Chem. A (IF=7.059) is out!
The effect of alkylammonium tail length in phenyl-alkyl spacer cations in quasi-2D Ruddlesden–Popper perovskites on the phase distribution in low n films (n = 2 stoichiometry) is investigated. An increase in alkyl chain length suppresses the formation of the n = 1 phase (and consequently higher n phases), which is attributed to the change in the packing arrangement of spacer cations from parallel (one and two carbon atom alkyl chains) to non-parallel (3 carbon atom alkyl chains). A single blue emission peak corresponding to the n = 3 phase (466 nm) and n = 2 phase (436 nm) is obtained in the PL spectra of phenylpropylammonium quasi-2D perovskites with methylammonium (MA) and formamidinium (FA) cations, respectively. The same trends in phase distribution, namely a reduction in the proportion of the n = 1 phase with increasing alkyl chain length, are observed for both MA- and FA-based perovskites. However, FA-based samples exhibited higher crystallinity but worsened morphology (more pinholes) and less efficient funneling compared to MA-based samples. Consequently, efficient sky-blue LEDs with the highest EQE of 3.35% are obtained for PPA2MAPb2Br7 perovskite.
05/2020
NEW cluster nodes @RBI installed!
New equipment for theoretical calculations purchased by our 2DPEROEXLORE project is installed and ready to be used at Dept. of Theoretical Physics, RBI
05/2020
State-of-the-art XRPD machine installed at our partner institution Dept. of Physics, Faculty of Science, Zagreb
New XRPD is purchased in the scope of the Physics Department project for infrastructure support financed by the European Regional Development Fund, OP "Competitiveness and Cohesion" 2014 - 2020.
New structures waiting to be determined by this monster machine at our partner institution!
04/2020
Our newest papers on solve diverse complex nonlinear least square problems and tehe distribution function of relaxation time in EIS are published!
The Levenberg-Marquardt algorithm (LMA) is generally used to solve diverse complex nonlinear least square (CNLS) problems and is one of the most used algorithms to extract equivalent electrochemical circuit (EEC) parameters from electrochemical impedance spectroscopy (EIS) data. It is a well-known fact that the convergence properties of the algorithm can be boosted by applying limits on EEC parameter values. However, when EEC parameter values are low (i.e., of the order of magnitude of 10−4 or smaller), the applied limits increase the first derivatives approximation errors which occur when using a numerical Jacobian matrix. In this work, we discuss the importance of the Jacobian matrix in LMA and propose a design of a new EIS fitting engine. The new engine is based on a novel fitting scheme using limits and a symbolic Jacobian matrix instead of the numerical one, i.e. a strategy that has not yet been reported in any EIS study. We show that using a symbolic Jacobian matrix the algorithm convergence is superior to the one with a numerical Jacobian matrix. We also investigate how to improve poor convergence properties when we still have to use a numerical Jacobian matrix when analytic derivatives are not available.​
Determination of the distribution function of relaxation times (DFRT) is an approach that gives us more detailed insight into system processes, which are not observable by simple electrochemical impedance spectroscopy (EIS) measurements. DFRT maps EIS data into a function containing the timescale characteristics of the system under consideration. The extraction of such characteristics from noisy EIS measurements can be described by Fredholm integral equation of the first kind that is known to be ill-posed and can be treated only with regularization techniques. Moreover, since only a finite number of EIS data may actually be obtained, the above-mentioned equation appears as after application of a collocation method that needs to be combined with the regularization. In the present study, we discuss how a regularized collocation of DFRT problem can be implemented such that all appearing quantities allow symbolic computations as sums of table integrals. The proposed implementation of the regularized collocation is treated as a multi-parameter regularization. Another contribution of the present work is the adjustment of the previously proposed multiple parameter choice strategy to the context of DFRT problem. The resulting strategy is based on the aggregation of all computed regularized approximants, and can be in principle used in synergy with other methods for solving DFRT problem. We also report the results from the experiments that apply the synthetic data showing that the proposed technique successfully reproduced known exact DFRT. The data obtained by our techniques is also compared to data obtained by well-known DFRT software
03/2020
Laboratory for synthesis and crystallography of functional materials works at home
01/2020
Computational school, Trieste, Italy
Juraj attended Computational School on Electronic Excitations in Novel Materials Using the Yambo Code, in Trieste, Italy, where he learned about post-DFT simulations, in particular many-body perturbation theory (MBPT) approaches and the calculation of electronic and optical properties of materials.
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