A new Tl4.86Fe0.82Hf1.18(MoO4)6ternary molybdate: crystal structure and properties
| Autor: | Jibzema G. Bazarova, Sergei Yu. Stefanovich, Alexander P. Dudka, Bair G. Bazarov, Victoria G. Grossman, I. A. Verin, N. E. Novikova |
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| Rok vydání: | 2020 |
| Předmět: |
Metals and Alloys
Crystal structure Activation energy Molybdate Atmospheric temperature range 010402 general chemistry 010403 inorganic & nuclear chemistry 01 natural sciences Atomic and Molecular Physics and Optics 0104 chemical sciences Electronic Optical and Magnetic Materials chemistry.chemical_compound Crystallography Octahedron chemistry Local symmetry Materials Chemistry Rectangular potential barrier Ternary operation |
| Zdroj: | Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials. 76:839-849 |
| ISSN: | 2052-5206 |
| Popis: | Single crystals of Tl4.86Fe0.82Hf1.18(MoO4)6[a=b= 10.5550 (3),c= 37.7824 (9) Å, γ = 120°] are obtained by the self-flux method in the Tl2MoO4–Fe2(MoO4)3–Hf(MoO4)2system. On the differential scanning calorimetry curve in the temperature range 320–350 K and atT∼ 690 K, endothermic peaks are observed. The second harmonic generation test shows an excess of the signal of the quartz standard by almost three times at room temperature. In the range 320–340 K its intensity decreases by almost three times and atT∼ 700 K it drops to zero. In the same interval, the temperature dependences of the unit-cell parameters and volume show stepwise changes. According to the X-ray diffraction data, the crystal structure consists of nonpolar and polar domains with different local symmetries. The structure is a three-dimensional framework consisting of alternating (Hf,Fe)O6octahedra connected by MoO4tetrahedra. Hf and Fe atoms occupy mixed Hf/Fe positions with different probabilities: 0.77:0.23, 0.50:0.50 and 0.32:0.68. Tl cations are located inside the framework in zigzag channels extended along theaandbaxes. The thallium arrangement is disordered,i.e.it involves additional positions and vacancies. The complex crystal structure has been solved using the nonstandard space groupR1, taking into account the local symmetryR3cfor the Mo atoms and mixed Hf/Fe positions mainly occupied by Hf atoms. The possible paths of ion transport are analyzed. The energy required to overcome the potential barrier between sites of Tl cations to migrate, which corresponds to the activation energy of conductivity, is estimated. The ion current is shown to be most probable in theabplane. |
| Databáze: | OpenAIRE |
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