Effect of Grain Size on Pressure-Induced Structural Transition in Mn₃O₄

Abstract

High-pressure researches on nanostructural material have been of considerable interest because of the appearance of many novel high-pressure behaviors in the nanomaterials. 1À4 Previous highpressure studies on nanocrystalline materials show that the grain size, shape, and structure of the nanocrystals have significant effects on the phase transition pressure, compressibility, and even phase transition routines, 5,6 in which, the size effect of nanomaterials has been found to be the most important factor all along and has attracted great enthusiasm. Many typical nanomaterials have been studied, such as ZnO, 7 TiO 2 , 8 CeO 2 , 9 ZnS, 10 Si, 11 and so on, and the size effects are found to influence their high-pressure behaviors, including the mechanical properties and transformations under pressure. Swamy et al. 12 studied nanocrystalline anatase TiO 2 using the high-pressure method and found a size-dependent phase selectivity of anatase at high pressure. All of these results show that nanomaterials give birth to distinct, usually enhanced, properties compared with conventional bulk polycrystalline materials. Therefore performing high-pressure studies on nanomaterials is important not only for exploring the new structures and properties in materials but also for fundamental scientific contribution, for example, understanding the factors that lead to phase transitions in materials. Spinels with AB 2 O 4 formula are binary oxides, which have important technological applications, including use as magnetic materials, 13 superhard materials, 14 and high-temperature ceramics. 15 Various spinel structures result from the different cation distributions in the A (tetrahedral) and B (octahedral) sites. 16 Highpressure studies on this family (mainly on bulk materials) have found three proposed orthorhombic phases of CaMn 2 O 4 -, CaTi 2 O 4 -, and CaFe 2 O 4 -type structures as high-pressure polymorphs of spinels. 17 Recently, Mao et al. compared the compressional behaviors of bulk and nanorod LiMn 2 O 4 and revealed that nanostructured materials can accommodate more stress compared with their bulk counterparts and make the nanomaterials possibly have enhanced application in battery. To our knowledge, this is the first high-pressure study on AB 2 O 4 formula nanomaterials. Therefore it is also expected the nanosize effect could alter compressibility, transition pressures, and even phase transformation routines for other members in the AB 2 O 4 -type ABSTRACT: The size effect on structural transitions of Mn 3 O 4 has been investigated under pressures by in situ synchrotron X-ray diffraction and Raman technique in a diamond anvil cell. Compared with bulk Mn 3 O 4 , Mn 3 O 4 nanoparticles show an obvious elevation of phase transition pressure and different phase transformation routines with the occurrence of a new high-pressure phase at 14.5À23.5 GPa. The new phase most probably has an orthorhombic CaTi 2 O 4 -type structure, which is regarded as a metastable phase transforming to the higher pressure marokite-like structure. By ...

Lifetime nanomanometry – high-pressure luminescence of up-converting lanthanide nanocrystals – SrF2:Yb3+,Er3+

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Structural Phase Transition and Compressibility of CaF2 Nanocrystals under High Pressure

“…Previous high-pressure studies on nanomaterials have revealed a set of novel high-pressure behaviors, which different from that of their corresponding bulk materials. The size effect has a great influence on the phase transition pressure [16][17][18][19], the course of amorphization [21][22][23][24][25], and phase transition routines [26]. Our previous high-pressure X-ray diffraction study revealed that CaF 2 nanocrystals with size of 8 nm transformed from fluorite structure into α-PbCl 2 -type structure at 14 GPa, and the high-pressure structure was stable up to 46.5 GPa.…”

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