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A new Tl4.86Fe0.82Hf1.18(MoO4)6 ternary molybdate: crystal structure and properties
Acta Crystallographica Section B ( IF 2.684 ) Pub Date : 2020-09-23 , DOI: 10.1107/s2052520620010768
Nataliya E. Novikova , Victoria G. Grossman , Bair G. Bazarov , Igor A. Verin , Alexander P. Dudka , Sergei Yu. Stefanovich , Jibzema G. Bazarova

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)2 system. On the differential scanning calorimetry curve in the temperature range 320–350 K and at T ∼ 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 at T ∼ 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)O6 octahedra connected by MoO4 tetrahedra. 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 the a and b axes. The thallium arrangement is disordered, i.e. it involves additional positions and vacancies. The complex crystal structure has been solved using the nonstandard space group R1, taking into account the local symmetry R3c for 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 the ab plane.

中文翻译:

一种新型的Tl4.86Fe0.82Hf1.18(MoO4)6三元钼酸盐:晶体结构和性质

在Tl 2 MoO中通过自流法获得了Tl 4.86 Fe 0.82 Hf 1.18(MoO 46 [ a = b = 10.5550(3),c = 37.7824(9)Å,γ= 120°]的单晶。4 –Fe 2(MoO 43 –Hf(MoO 42系统。在差示扫描量热曲线上,温度范围为320–350 K,在T约690 K,观察到吸热峰。二次谐波产生测试显示,在室温下,石英标样的信号超出了几乎三倍。范围为320-340ķ其强度几乎三次,并在降低Ť〜700ķ它下降到零。在相同的时间间隔中,晶胞参数和体积的温度依赖性显示逐步变化。根据X射线衍射数据,晶体结构由具有不同局部对称性的非极性和极性域组成。该结构是三维框架,由通过MoO 4连接的交替(Hf,Fe)O 6八面体组成四面体。Hf和Fe原子占据Hf / Fe混合位置的概率不同:0.77:0.23、0.50:0.50和0.32:0.68。T1阳离子位于沿ab轴延伸的之字形通道中的框架内。al的排列是无序的,涉及额外的位置和空位。考虑到局部对称性R 3 c,已经使用非标准空间群R 1解决了复杂的晶体结构对于Mo原子和主要由Hf原子占据的混合Hf / Fe位置。分析了离子传输的可能路径。估计了克服T1阳离子迁移位点之间的势垒所需的能量,其对应于电导率的活化能。离子电流显示出在ab平面中最有可能。
更新日期:2020-10-07
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