Structure Evolution Of Ti-based And Rear Earth-based Metallic Glasses Under High Pressure

Metallic glasses?MGs?,as a new member of glass family,have a disordered structure and exhibit uncommon properties,which stimulates widespread research interest in MGs.Polyamorphism in MGs is one of interest of research.Traditional network-forming glassy state materials,such as ice,silica and silicon have been reported to exhibit polyamorphism induced by pressure,which tends to be ascribed to an increase in atomic coordination.Whereas,metallic glasses are distinct from the traditional glasses due to the non-directional metallic bonds.Therefore,polyamorphism induced by pressure in metallic glass was supposed to be impossible for they are spatially densely-packing and have the maximum coordination number already.However,polyamorphic transitions were discovered in recent years.In this work,Pressure-induced polyamorphism in MGs was studied,including absence of polyamorphism as well as polyamorphism in lanthanides-solvent MGs and lanthanides-solute MGs.Summarily,the main results of the study are as follows:?1?The structure of binary Ti₆₂Cu₃₈ metallic glass was investigated under pressures up to 33.8 GPa using the pair distribution function?PDF?analysis based on the high energy X-ray scattering and reverse Monte Carlo?RMC?simulations.At global scale,its relative volume showed a continuously smooth curve as a function of pressure.The isothermal bulk modulus of Ti₆₂Cu₃₈ metallic glass was estimated as B0 = 132?3?GPa with B0' = 5.8?0.4?.At local scale,atomic packing structure under compression conditions,which was extracted from RMC simulations,showed that the topological short-range order was dominated by the deformed icosahedron polyhedra and basically maintained stable.From the relationship between relative volume and changing ratio of the atomic separation distances,the real space fractal dimensionality of this metallic glass was determined as about 2.5 for all of first four peaks,and this experimental result revealed the consistent nature of fractal feature on degree of self-similarity in this sample within the entire experimental pressure range.?2?The Yb-based metallic glass is investigated using synchrotron X-ray total scattering method under high pressure.The polyamorphic transformation from low density to high density is observed,accompanying with a volume collapse reflected by a discontinuousness of isothermal bulk modulus.This collapse is caused by that distortional icosahedron short range order precedes to perfect icosahedron,which might link to Yb 4f electron delocalization upon compression,and matches the result of in situ electrical resistance measurement under high pressure conditions.This discovery in Yb-based metallic glass,combined with the previous reports on other metallic glass systems,demonstrates that pressure induced polyamorphism is the general behavior for typical lanthanide-based metallic glasses.?3?Pressure induced polyamorphism in Yb-based metallic glass suggests the electronic structure inheritance of lanthanide-solvent atoms in lanthanide-based metallic.Is a polyamorphism possible in lanthanide-solute metallic glasses? So far,polyamorphic phase transitions in metallic glass containing lanthanide have been observed only in lanthanide-solvent metallic glasses.The lanthanide-solute metallic glass La_43.4Pr_18.6Al₁₄Cu₂₄ was studied using in situ X-ray total scattering method.Our results exhibit a polyamorphism transition induced by pressure in this selected lanthanide-solute metallic glass from LDAS to HDAS with large volume collapse,accompanying a local structure change from a distortional icosahedra to a more perfect one.The structure change is also reflected by P-r1 relation in short range length scale and P-Q1 relation in medium range length scale.Considering the impossibility of polyamorphism transformation in metallic glasses resulting from coordination increase and absence of 4f electron in lanthanum,the polyamorphic transformation in lanthanide-solute metallic glass is attributed to 4f electron delocalization in Pr element.Thus,not only lanthanide-solvent but also lanthanide-solute metallic glasses inherit electronic structure from lanthanide.This discovery offers a supplement to research on lanthanide-based metallic glasses,which further provides a new perspective of the polyamorphic transformation in metallic glasses containing lanthanide element.In sumary,this wrok firstly provides evidence in experiment that the scaling power 2.5 extends beyond the first peak in metalic glass.Furthermore,the pressure-induced polyamorphic transformation in Yb-based metallic glass suggests that polyamorphism under pressure is the general behavior for typical lanthanide-based metallic glasses.This result also proves the electronic structure inheritance of lanthanide-solvent atoms in lanthanide-based metallic.Pressure-induced polyamorphic transtion in La_43.4Pr_18.6Al₁₄Cu₂₄ indicates the inheritance of electronic structure from lanthanide-solute atom.These results advande the high pressure research and provide a new perspective of study on metallic glasses.