Zero thermal expansion in cubic MgZrF₆

Abstract

Isotropic zero thermal expansion (ZTE) is rare but intriguing physical property in materials. Here, we report an isotropic ZTE property in a double ReO3‐type compound of MgZrF6, which exhibits a negligible value of coefficient of thermal expansion (αl = −7.94 × 10−7 K−1 (XRD), αl = −4.22 × 10−7 K−1 (dilatometry), 300‐675 K). The ZTE mechanism of MgZrF6 is understood by the joint studies of temperature dependence of crystal structure and lattice dynamics. Interestingly, different magnitudes of atomic displacement parameters (ADPs) for the fluorine atoms in MZrF6 (M = Ca, Ni, Mg) are found. The strong temperature sensitivity of ADPs demonstrates intensive transverse thermal vibration of fluorine atoms, which contributes essentially to the negative thermal expansion of CaZrF6. By contrast, for NiZrF6 with positive thermal expansion, the temperature response of ADPs is weak. Moderate transverse thermal vibration takes place in MgZrF6, and ZTE appears. Furthermore, lattice dynamics of MgZrF6 is studied by temperature‐dependent Raman spectroscopy, which reveals the ZTE mechanism. In particular, the F2g and Ag modes, corresponding to the bending and stretching vibrations of fluorine atoms, respectively, neither soften nor harden over the whole temperature range, which is correlated with the isotropic ZTE property of MgZrF6.

Negative thermal expansion behavior in MZrF6(M=Ca,Mg,Sr) : Ab initio lattice dynamical stu

“…We have compared the calculated fractional volume change with available experimental values in Fig 6 . The thermal expansion behaviour of MgZrF6 shows very good agreement with the availbale experimental data [28]. The experminetal data of SrZrF6 are not availbale.…”

Intrinsic Isotropic Near-Zero Thermal Expansion in Zn4B6O12X (X = O, S, Se)

“…1.540(5)/MK, and 1.554(2)/MK, respectively. These CTE values are much lower than those in the majority of materials, and thus the three compounds can be categorized as the near-ZTE materials, with the linear CTE comparable to other ever-reported ZTE materials, such as MgZrF 6 (−0.79/MK, 300–675 K), Fe­[Co­(CN) 6 ] (−1.47/MK, 4.2–300 K), TaO 2 F (0.6/MK, 200–773 K), and K 6 Cd 3 (C 3 N 3 O 3 ) 4 (0.06/MK, 10–130 K). In particular, the cell parameters of ZBO, ZBS, and ZBSe are almost persistent between 5 and 200 K with the linear CTE of 0.651(1)/MK, 0.593(2)/MK, and 0.642(1)/MK, respectively, and the materials can be categorized into the ZTE class.…”

“…The achievement of intrinsic ZTE in perfect lattices is a very tough task since it is extremely difficult to obtain the subtle balance between the thermal expansion and contraction without external regulation. Moreover, for practical purposes, it is convenient to require the isotropic ZTE materials. − To our best knowledge, the intrinsic isotropic ZTE behavior has only been observed in a handful of materials, including Fe­[Co­(CN) 6 ], TaO 2 F, MgZrF 6 , and K 6 Cd 3 (C 3 N 3 O 3 ) 4 . Therefore, the research is highly desirable on the exploration of new intrinsic isotropic ZTE materials and the understanding of the underlying mechanisms. − …”

“…Moreover, for practical purposes, it is convenient to require the isotropic ZTE materials. 11−13 To our best knowledge, the intrinsic isotropic ZTE behavior has only been observed in a handful of materials, including Fe[Co(CN) 6 ], 14 TaO 2 F, 15 MgZrF 6 , 11 and K 6 Cd 3 (C 3 N 3 O 3 ) 4 . 16 Therefore, the research is highly desirable on the exploration of new intrinsic isotropic ZTE materials and the understanding of the underlying mechanisms.…”

Mn(IV)‐Substituted Metal(II) Hexafluorido Metallates(IV): Synthesis, Crystal Structures, and Luminescence Properties

“…To the best of our knowledge no crystal structure has been reported so far for MgHfF 6 . However, the certainly closely related compound MgZrF 6 is known to be dimorphic and crystallizes both in the NaSbF 6 and LiSbF 6 structure types [42–45] . We performed powder X‐ray diffraction analysis on a sample which contained MgHfF 6 , HfF 4 , and MgF 2 .…”