Abstract
The interface effect is one of the most important factors that strongly affect the structural transformations and the properties of nano-/submicro-crystals under pressure. However, characterization of the granular boundary changes in materials is always challenging. Here, using tetrakaidecahedral Zn2SnO4 microcrystals as an example, we employed alternating current impedance, X-ray diffraction methods and transmission electron microscopy to elucidate the effect of the interface on the structure and electrical transport behavior of the Zn2SnO4 material under pressure. We clearly show that grain refinement of the initial microcrystals into nanocrystals (approximately 5 nm) occurs at above 12.5 GPa and is characterized by an anomalous resistance variation without a structural phase transition. A new phase transition pathway from the cubic to hexagonal structure occurs at approximately 29.8 GPa in Zn2SnO4. The unexpected grain refinement may explain the new structural transition in Zn2SnO4, which is different from the previous theoretical prediction. Our results provide new insights into the link between the structural transition, interface changes and electrical transport properties of Zn2SnO4.
Highlights
The Fd3m space group[11,12,13]
Alternating current (AC) impedance spectroscopy is an effective technique for the detection of the changes at the grain boundary or the interface upon compression and can be used to study the related property changes by measuring the boundary transport behaviors such as the boundary resistance
Using the Rietveld refinement analysis implemented in the GSAS program, the diffraction pattern obtained at ambient pressure was found to be well-indexed by a cubic structure with the Fd3m space group
Summary
The tetrakaidecahedral ZTO single crystals were synthesized by a hydrothermal method[16]. For direct comparison with previous studies, we first conducted high-pressure XRD experiments on tetrakaidecahedral ZTO single crystals for pressures up to 49.1 GPa with silicone oil as the pressure-transmitting medium (PTM). It is clear that the XRD pattern agrees well with that obtained when using silicone oil as the PTM, the phase transition occurs at approximately 29.8 GPa. our Rietveld refinement analysis of the high pressure pattern suggests that all the peaks of the new phase can be indexed by a hexagonal structure (Fig. 3c). 14, in which transformations into an intermediate phase at 12.9 GPa and into an orthorhombic structure at above 32.7 GPa were observed This difference in the phase transitions can be attributed to the different crystal sizes and morphologies of the ZTO samples used in the two experiments. We used AC impedance measurements and HRTEM to explore the underlying changes in the ZTO sample
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