Abstract
The phase formation in the boron-rich section of the Al-Y-B system has been explored by a correlative theoretical and experimental research approach. The structure of coatings deposited via high power pulsed magnetron sputtering from a compound target was studied using elastic recoil detection analysis, electron energy loss spectroscopy spectrum imaging, as well as X-ray and electron diffraction data. The formation of AlYB14 together with the (Y,Al)B6 impurity phase, containing 1.8 at. % less B than AlYB14, was observed at a growth temperature of 800 °C and hence 600 °C below the bulk synthesis temperature. Based on quantum mechanical calculations, we infer that minute compositional variations within the film may be responsible for the formation of both icosahedrally bonded AlYB14 and cubic (Y,Al)B6 phases. These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions.
Highlights
INTRODUCTIONIcosahedral boron-rich solids exhibit outstanding physical properties, such as high hardness at low density,[1,2,3,4] high wear resistance,[5] high stiffness,[6,7,8] extremely high melting point,[1] thermal stability,[2] exceptional tolerance against radiation damage,[2] and high Seebeck coefficient.[9,10,11] Such properties render these materials suitable for many applications, e.g., neutron absorber in nuclear reactors,[9] energy conversion,[2,9,11] and protective coatings.[1,2,12,13] These properties are enabled by the presence of a B icosahedra network in these solids
These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions
The sample deposited at 800 C was measured by Time-Of-Flight Elastic Recoil Detection Analysis (TOFERDA) and used as a standard for the energy dispersive X-ray (EDX) measurements
Summary
Icosahedral boron-rich solids exhibit outstanding physical properties, such as high hardness at low density,[1,2,3,4] high wear resistance,[5] high stiffness,[6,7,8] extremely high melting point,[1] thermal stability,[2] exceptional tolerance against radiation damage,[2] and high Seebeck coefficient.[9,10,11] Such properties render these materials suitable for many applications, e.g., neutron absorber in nuclear reactors,[9] energy conversion,[2,9,11] and protective coatings.[1,2,12,13] These properties are enabled by the presence of a B icosahedra network in these solids. Attempts to grow AlMgB14 thin films by pulsed laser deposition[15] and magnetron sputtering (MS)[26] both at temperatures of 600 C resulted in the formation of X-ray amorphous structures. AlMg compound target which was operated in DC mode and two B targets which were according to the authors sputtered using 350 kHz pulses.[28] This is the first report on the direct synthesis of crystalline AlMgB14 at a temperature of 200 C.28. Multiple diffraction peaks from the AlMgB14-phase should be expected Both of the above discussed diffraction data sets[28] leave room for alternative phase formation scenarios as presented by the authors.[28]. HPPMS is a prolific provider of ions formed from the sputter gas as well as from the sputtered and film forming species.[41,42]
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