Understanding Negative Thermal Expansion of Zn₂GeO₄ through Local Structure and Vibrational Dynamics

Abstract

Zn2GeO4 is a multifunctional material whose intrinsic thermal expansion properties below ambient temperature have not been explored until now. Herein, the thermal expansion of Zn2GeO4 is investigated by synchrotron X-ray diffraction, with the finding that Zn2GeO4 exhibits very low negative (αv = −2.02 × 10–6 K–1, 100–300 K) and positive (αv = +2.54 × 10–6 K–1, 300–475 K) thermal expansion below and above room temperature, respectively. A combined study of neutron powder diffraction and extended X-ray absorption fine structure spectroscopy shows that the negative thermal expansion (NTE) of Zn2GeO4 originates from the transverse vibrations of O atoms in the four- and six-membered rings with ZnO4–GeO4 tetrahedra. In addition, the results of temperature- and pressure-dependent Raman spectra identify the low-frequency phonon modes (50–150 cm–1) with negative Grüneisen parameters softening upon pressuring and stiffening upon heating during the lattice contraction, thus contributing to the NTE. This study not only reports the interesting thermal expansion behavior of Zn2GeO4 but also provides further insights into the NTE mechanism of novel structures.

Chemical Diversity for Tailoring Negative Thermal Expansion

“…The revelation of the actual bond length from the characterization methods of local structure and the clarification for the abnormal lattice NTE provide realistic insight into structure tailoring. A similar structural mechanism also provides a general explanation for the NTE behaviors in compounds with prominent transverse vibration, including CuScO 2 , ZnGeO 4 , and Prussian-blue analogues like Zn­(CN) 2 …”

Tailoring of Upconversion Emission in Tm3+/Yb3+-Codoped Y2Mo3O12 Submicron Particles Via Thermal Stimulation Engineering for Non-invasive Thermometry

“…Therefore, more effort ought to be made so as to settle these issues. To date, negative thermal expansion (NTE) compounds, whose lattice volumes decline at elevated temperature, have been intensively studied owing to their feasibility in manipulating the thermal expansion effect. , Interestingly, via use of the NTE effect of ScF 3 and Sc 2 Mo 3 O 12 , Wang et al first observed the thermally enhanced UC emissions in ScF 3 :Er 3+ /Yb 3+ and Sc 2 Mo 3 O 12 :Ho 3+ /Yb 3+ compounds due to the improved ET from Yb 3+ to other rare-earth ions (i.e., Er 3+ , Ho 3+ ) trigged by the lattice contraction. , Hence, the employment of NTE compounds as a luminescent host for rare-earth ions would be an efficient route to resist the thermal quenching effect of rare-earth ion-doped upconverting materials.…”

Origin of Near-Zero Thermal Expansion in A2O(PO4)2 Oxides over an Ultrawide Temperature Range

“…The MSDs parallel to the bond direction are very small, just like Zn 2 GeO 4 . 55 Differently, the MSDs perpendicular to the bond direction are much larger, in particular that of the twofold coordinated O atom is larger than that of three-fold coordinated; therefore, the former is more flexible as we expected. Moreover, the perpendicular MSD of O atoms decreases sequentially, i.e., Th 2 O(PO 4 ) 2 > U 2 O(PO 4 ) 2 > Zr 2 O(PO 4 ) 2 > Hf 2 O(PO 4 ) 2 , implying a progressive decrease in the transverse vibrations of O atoms, like the order of the AAV.…”