Browsing by Author "Garmonov, Alexander A."

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    A challenge toward novel quaternary sulfides SrLnCuS3 (Ln = La, Nd, Tm) : unraveling synthetic pathways, structures and properties
    (2022) Ruseikina, Anna V.; Grigoriev, Maxim V.; Solovyov, Leonid A.; Chernyshev, Vladimir A.; Aleksandrovsky, Aleksandr S.; Krylov, Alexander S.; Krylova, Svetlana N.; Shestakov, Nikolai P.; Velikanov, Dmitriy A.; Garmonov, Alexander A.; Matigorov, Alexey V.; Eberle, Marcel A.; Schleid, Thomas; Safin, Damir A.
    We report on the novel heterometallic quaternary sulfides SrLnCuS3 (Ln = La, Nd, Tm), obtained as both single crystals and powdered samples. The structures of both the single crystal and powdered samples of SrLaCuS3 and SrNdCuS3 belong to the orthorhombic space group Pnma but are of different structural types, while both samples of SrTmCuS3 crystallize in the orthorhombic space group Cmcm with the structural type KZrCuS3. Three-dimensional crystal structures of SrLaCuS3 and SrNdCuS3 are formed from the (Sr/Ln)S7 capped trigonal prisms and CuS4 tetrahedra. In SrLaCuS3, alternating 2D layers are stacked, while the main backbone of the structure of SrNdCuS3 is a polymeric 3D framework [(Sr/Ln)S7]n, strengthened by 1D polymeric chains (CuS4)n with 1D channels, filled by the other Sr2+/Ln3+ cations, which, in turn, form 1D dimeric ribbons. A 3D crystal structure of SrTmCuS3 is constructed from the SrS6 trigonal prisms, TmS6 octahedra and CuS4 tetrahedra. The latter two polyhedra are packed together into 2D layers, which are separated by 1D chains (SrS6)n and 1D free channels. In both crystal structures of SrLaCuS3 obtained in this work, the crystallographic positions of strontium and lanthanum were partially mixed, while only in the structure of SrNdCuS3, solved from the powder X-ray diffraction data, were the crystallographic positions of strontium and neodymium partially mixed. Band gaps of SrLnCuS3 (Ln = La, Nd, Tm) were found to be 1.86, 1.94 and 2.57 eV, respectively. Both SrNdCuS3 and SrTmCuS3 were found to be paramagnetic at 20-300 K, with the experimental magnetic characteristics being in good agreement with the corresponding calculated parameters.
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    Quaternary selenides EuLnCuSe3 : synthesis, structures, properties and in silico studies
    (2022) Grigoriev, Maxim V.; Solovyov, Leonid A.; Ruseikina, Anna V.; Aleksandrovsky, Aleksandr S.; Chernyshev, Vladimir A.; Velikanov, Dmitriy A.; Garmonov, Alexander A.; Molokeev, Maxim S.; Oreshonkov, Aleksandr S.; Shestakov, Nikolay P.; Matigorov, Alexey V.; Volkova, Svetlana S.; Ostapchuk, Evgeniy A.; Kertman, Alexander V.; Schleid, Thomas; Safin, Damir A.
    In this work, we report on the synthesis, in-depth crystal structure studies as well as optical and magnetic properties of newly synthesized heterometallic quaternary selenides of the Eu+2Ln+3Cu+1Se3 composition. Crystal structures of the obtained compounds were refined by the derivative difference minimization (DDM) method from the powder X-ray diffraction data. The structures are found to belong to orthorhombic space groups Pnma (structure type Ba2MnS3 for EuLaCuSe3 and structure type Eu2CuS3 for EuLnCuSe3, where Ln = Sm, Gd, Tb, Dy, Ho and Y) and Cmcm (structure type KZrCuS3 for EuLnCuSe3, where Ln = Tm, Yb and Lu). Space groups Pnma and Cmcm were delimited based on the tolerance factor t’, and vibrational spectroscopy additionally confirmed the formation of three structural types. With a decrease in the ionic radius of Ln3+ in the reported structures, the distortion of the (LnCuSe3) layers decreases, and a gradual formation of the more symmetric structure occurs in the sequence Ba2MnS3 → Eu2CuS3 → KZrCuS3. According to magnetic studies, compounds EuLnCuSe3 (Ln = Tb, Dy, Ho and Tm) each exhibit ferrimagnetic properties with transition temperatures ranging from 4.7 to 6.3 K. A negative magnetization effect is observed for compound EuHoCuSe3 at temperatures below 4.8 K. The magnetic properties of the discussed selenides and isostructural sulfides were compared. The direct optical band gaps for EuLnCuSe3, subtracted from the corresponding diffuse reflectance spectra, were found to be 1.87-2.09 eV. Deviation between experimental and calculated band gaps is ascribed to lower d states of Eu2+ in the crystal field of EuLnCuSe3, while anomalous narrowing of the band gap of EuYbCuSe3 is explained by the low-lying charge-transfer state. Ab initio calculations of the crystal structures, elastic properties and phonon spectra of the reported compounds were performed.
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    ItemOpen Access
    Single crystals of EuScCuSe3 : synthesis, experimental and DFT investigations
    (2023) Grigoriev, Maxim V.; Ruseikina, Anna V.; Chernyshev, Vladimir A.; Oreshonkov, Aleksandr S.; Garmonov, Alexander A.; Molokeev, Maxim S.; Locke, Ralf J. C.; Elyshev, Andrey V.; Schleid, Thomas
    EuScCuSe3 was synthesized from the elements for the first time by the method of cesium-iodide flux. The crystal belongs to the orthorhombic system (Cmcm) with the unit cell parameters a = 3.9883(3) Å, b = 13.2776(9) Å, c = 10.1728(7) Å, V = 538.70(7) Å3. Density functional (DFT) methods were used to study the crystal structure stability of EuScCuSe3 in the experimentally obtained Cmcm and the previously proposed Pnma space groups. It was shown that analysis of elastic properties as Raman and infrared spectroscopy are powerless for this particular task. The instability of EuScCuSe3 in space group Pnma space group is shown on the basis of phonon dispersion curve simulation. The EuScCuSe3 can be assigned to indirect wide-band gap semiconductors. It exhibits the properties of a soft ferromagnet at temperatures below 2 K.
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    Synthesis, crystal structure and properties of the new laminar quaternary tellurides SrLnCuTe3 (Ln = Sm, Gd-Tm and Lu)
    (2023) Ruseikina, Anna V.; Grigoriev, Maxim V.; Molokeev, Maxim S.; Garmonov, Alexander A.; Elyshev, Andrey V.; Locke, Ralf J. C.; Schleid, Thomas
    This paper reports for the first time on the new laminar quaternary orthorhombic heterometallic quaternary tellurides SrLnCuTe3, the fabrication of which has been a challenge until this work. Data on the crystal structure of tellurides complete the series of quaternary strontium chalcogenides SrLnCuCh3 (Ch = S, Se, Te). Single crystals of the compounds were synthesized from the elements by the halogenide-flux method at 1070 K. The compounds are crystallizing in two space groups Pnma (Ln = Sm, Gd and Tb) and Cmcm (Ln = Dy-Tm and Lu). For SrSmCuTe3 (a = 11.4592(7), b = 4.3706(3), c = 14.4425(9) Å, space group: Pnma) with the largest lanthanoid cation, Sr2+ shows C.N. = 7, whereas Sm3+ reveals a diminished coordination number C.N. = 6. For SrLuCuTe3 (a = 4.3064(3), b = 14.3879(9), c = 11.1408(7) Å, space group: Cmcm) with the smallest lanthanoid cation, coordination numbers of six are realized for both high-charged cations (Sr2+ and Lu3+: C.N. = 6). The cations Sr2+, Ln3+, Cu+ each take independent positions. The structures are built by distorted [CuTe4]7- tetrahedra, forming the infinite chains {∞1[Cu(Te1)1/1t(Te2)1/1t(Te3)2/2e]5−} along [010] in SrLnCuTe3 (Ln = Sm, Gd and Tb) and [100] in SrLnCuTe3 (Ln = Dy-Tm and Lu). The distortion of the polyhedra [CuTe4]7- was compared for the whole series SrLnCuTe3 by means of τ4-descriptor for the four coordinating Te2- anions, which revealed a decrease in the degree of distortion with a decreasing radius at Ln3+. The distorted octahedra [LnTe6]9- form layers {∞2[Ln(Te1)2/2(Te2)2/2(Te3)2/2]3−}. The distorted octahedra and tetrahedra fuse to form parallel layers {∞2[CuLnTe3]2−} and between them, the Sr2+ cations providing three-dimensionality of the structure are located. In the SrLnCuTe3 (Ln = Sm, Gd and Tb) structures, the Sr2+ cations center capped the trigonal prisms [SrTe6+1]12−, united in infinite chains {∞1[Sr(Te1)2/2(Te2)3/3(Te3)2/2]4−} along the [100] direction. The domains of existence of the Ba2MnS3, BaLaCuS3, Eu2CuS3 and KZrCuS3 structure types are defined in the series of orthorhombic chalcogenides SrLnCuCh3 (Ch = S, Se and Te). The tellurides SrLnCuTe3 (Ln = Tb-Er) of both structure types in the temperature range from 2 up to 300 K are paramagnetic, without showing clear signs of a magnetic phase transition.
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    Synthesis, crystal structure, and optical and magnetic properties of the new quaternary erbium telluride EuErCuTe3 : experiment and calculation
    (2024) Ruseikina, Anna V.; Grigoriev, Maxim V.; Locke, Ralf J. C.; Chernyshev, Vladimir A.; Garmonov, Alexander A.; Schleid, Thomas
    This paper reports for the first time on a new layered magnetic heterometallic erbium telluride EuErCuTe3. Single crystals of the compound were obtained from the elements at 1120 K using CsI as a flux. The crystal structure of EuErCuTe3 was solved in the space group Cmcm (a = 4.3086(3) Å, b = 14.3093(9) Å, and c = 11.1957(7) Å) with the KZrCuS3 structure type. In the orthorhombic structure of erbium telluride, distorted octahedra ([ErTe6]9−) form two-dimensional layers (Er(Te1)2/2e(Te2)4/2k-)∞2, while distorted tetrahedra ([CuTe4]7-) form one-dimensionally connected substructures (Cu(Te1)2/2e(Te2)2/1t5-∞1) along the [100] direction. The distorted octahedra and tetrahedra form parallel two-dimensional layers (CuErTe32-∞2) between which Eu2+ ions are located in a trigonal-prismatic coordination environment (EuTe610-). The trigonal prisms are connected by faces, forming chains (Eu(Te1)2/2(Te2)4/22-∞1) along the [100] direction. Regularities in the variations in structural parameters were established in the series of erbium chalcogenides (EuErCuCh3 with Ch = S, Se, and Te) and tellurides (EuLnCuTe3 with Ln = Gd, Er, and Lu). Ab-initio calculations of the crystal structure, phonon spectrum, and elastic properties of the compound EuErCuTe3 were performed. The types and wavenumbers of fundamental modes were determined, and the involvement of ions in the IR and Raman modes was assessed. The experimental Raman spectra were interpreted. The telluride EuErCuTe3 at temperatures below 4.2 K was ferrimagnetic, as were the sulfide and selenide derivatives (EuErCuCh3 with Ch = S and Se). Its experimental magnetic characteristics were close to the calculated ones. The decrease in the magnetic phase transition temperature in the series of the erbium chalcogenides was discovered.