Zaraq Asmaa, Orayech Brahim, Igartua Josu M, El Bouari Abdeslam, Gregory Duncan H, Gesing Thorsten M
University of Bremen, Institute of Inorganic Chemistry and Crystallography, Bremen, Germany.
Maxam, Technology Center Energetic Materials, Carretera N-623 km 28, 09141Quintanilla Sobresierra, Burgos, Spain.
Dalton Trans. 2023 Mar 28;52(13):4086-4102. doi: 10.1039/d2dt03543j.
Polycrystalline double perovskite-type Sr(CoFe)TeO with various stoichiometric compositions ( = 0, 0.25, 0.5, 0.75, and 1) were synthesized by solid-state reactions in air. The crystal structures and phase transitions of this series at different temperature intervals were determined by X-ray powder diffraction, and from the obtained data the crystal structures were refined. It has been proven that for the compositions = 0.25, 0.50, and 0.75, the phases crystallize at room temperature in the monoclinic space group 2/. Down to 100 K, depending on the composition, these structures experience a phase transition from 2/ to 2/. At high temperatures up to 1100 K their crystal structures show two further phase transitions. The first one is a first-order phase transition, from monoclinic 2/ to tetragonal 4/, followed by a second-order phase transition to cubic 3̄. Therefore, the phase transition sequence of this series detected at temperatures ranging from 100 K to 1100 K is 2/ → 2/ → 4/ → 3̄. The temperature-dependent vibrational features of the octahedral sites were investigated by Raman spectroscopy, which furthermore complements the XRD results. A decrease in the phase-transition temperature with increasing iron content has been observed for these compounds. This fact is explained by the progressive diminishing of the distortion of the double-perovskite structure in this series. Using room-temperature Mössbauer spectroscopy, the presence of two iron sites is confirmed. The two different transition metal cations Co and Fe at the B sites allow exploring their effect on the optical band-gap.
通过在空气中进行固态反应合成了具有不同化学计量组成（= 0、0.25、0.5、0.75和1）的多晶双钙钛矿型Sr(CoFe)TeO。通过X射线粉末衍射确定了该系列在不同温度区间的晶体结构和相变，并根据所得数据对晶体结构进行了精修。已证明，对于组成= 0.25、0.50和0.75的情况，这些相在室温下在单斜空间群2/中结晶。降至100 K时，根据组成不同，这些结构会经历从2/到2/的相变。在高达1100 K的高温下，它们的晶体结构还显示出另外两个相变。第一个是一级相变，从单斜2/到四方4/，接着是二级相变到立方3̄。因此，在100 K至1100 K温度范围内检测到的该系列的相变顺序为2/ → 2/ → 4/ → 3̄。通过拉曼光谱研究了八面体位置随温度变化的振动特征，这进一步补充了XRD结果。已观察到这些化合物的相变温度随铁含量的增加而降低。这一事实可通过该系列中双钙钛矿结构畸变的逐渐减小来解释。使用室温穆斯堡尔光谱证实了存在两个铁位点。B位点上两种不同的过渡金属阳离子Co和Fe使得能够探究它们对光学带隙的影响。
