Rahimi Mosafer Houri S, Paszkowicz Wojciech, Minikayev Roman, Kozłowski Mirosław, Diduszko Ryszard, Berkowski Marek
Institute of Physics, Polish Academy of Sciences, Warsaw, Poland.
Dalton Trans. 2021 Oct 26;50(41):14762-14773. doi: 10.1039/d1dt02446a.
The whitlockite-related materials have attracted researchers' attention because of their potential application in various fields, especially in optoelectronics. In the present work, the structure of novel whitlockite-related oxides CaTM(VO) (TM = Co, Cu) is studied at room and high temperatures, using X-ray powder diffraction. These compounds form by fractional substitution of divalent transition metal atoms into the Ca(VO) lattice. Rietveld refinements provided the structural details. The lattice parameters are = 10.78074(6) Å, = 37.8196(2) Å, and = 3806.67(4) Å for CaCo(VO) and = 10.78710(7) Å, = 37.8997(3) Å, and = 3819.23(4) Å for CaCu(VO). Structure refinement results show that among the five available sites (M1-M5), the M ions select the M5 site. This finding is confirmed by analysis of interatomic distances: due to the difference in size between TM and Ca ions sharing the M5 site, the M5-O distance shortens by about 5.0% for CaCo(VO) and 2.7% for CaCu(VO) with respect to the unsubstituted parent compound, Ca(VO). The observed trends in the crystallographic properties of the studied crystals are in line with those of previously reported structurally related phosphates, CaM(PO) (M = Mg or divalent transition metal). Moreover, the observed tendency for occupation of M5 by small divalent ions follows the earlier theoretical results. For cobalt and copper substituted orthovanadate and orthophosphate whitlockite related materials, a linear variation in the unit cell size is demonstrated. The common equation for evaluation of volume is applicable to the substitution of the two transition metals in orthovanadate and orthophosphate whitlockite related materials. Thermal expansion is investigated for both compounds. The variations of the lattice parameters and the thermal expansion coefficient with temperature are determined in the 300-810 K range. The lattice parameter, , expands by 0.80% for CaCo(VO) and 0.74% for CaCu(VO) in this range. The lattice parameter, , enlarges by about 0.70% for both samples. In the studied temperature range, the volume thermal expansion coefficient of CaCo(VO) increases from 37.2 to 44.8 MK and for CaCu(VO), it increases from 35.1 to 45.2 MK; the observed expansion anisotropy is smaller than those of other related compounds.
与白磷钙矿相关的材料因其在各个领域，尤其是光电子学领域的潜在应用而引起了研究人员的关注。在本工作中，利用X射线粉末衍射研究了新型白磷钙矿相关氧化物CaTM(VO)（TM = Co、Cu）在室温和高温下的结构。这些化合物通过二价过渡金属原子部分取代进入Ca(VO)晶格而形成。Rietveld精修提供了结构细节。对于CaCo(VO)，晶格参数为 = 10.78074(6) Å、 = 37.8196(2) Å、 = 3806.67(4) Å；对于CaCu(VO)，晶格参数为 = 10.78710(7) Å、 = 37.8997(3) Å、 = 3819.23(4) Å。结构精修结果表明，在五个可用位点（M1 - M5）中，M离子选择M5位点。这一发现通过原子间距离分析得到证实：由于共享M5位点的TM和Ca离子尺寸不同，相对于未取代的母体化合物Ca(VO)，CaCo(VO)的M5 - O距离缩短约5.0%，CaCu(VO)的缩短2.7%。在所研究晶体的晶体学性质中观察到的趋势与先前报道的结构相关的磷酸盐CaM(PO)（M = Mg或二价过渡金属）的趋势一致。此外，观察到的小二价离子占据M5位点的趋势与早期理论结果相符。对于钴和铜取代的原钒酸盐和原磷酸盐白磷钙矿相关材料，证明了晶胞尺寸呈线性变化。评估体积的通用方程适用于原钒酸盐和原磷酸盐白磷钙矿相关材料中两种过渡金属的取代。对这两种化合物都进行了热膨胀研究。在300 - 810 K范围内测定了晶格参数和热膨胀系数随温度的变化。在此范围内，CaCo(VO)的晶格参数 膨胀了0.80%，CaCu(VO)的膨胀了0.74%。两个样品的晶格参数 都增大了约0.70%。在所研究的温度范围内，CaCo(VO)的体积热膨胀系数从37.2增加到44.8 MK，CaCu(VO)的从35.1增加到45.2 MK；观察到的膨胀各向异性小于其他相关化合物。
