Diffraction studies in non crystalline systems
Diffraction studies in non crystalline systems
Diffraction studies in non crystalline systems
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Elements of ref<strong>in</strong>ement - BackgroundSmoothInelastic and resonantStructuredThermal Disorder Scatter<strong>in</strong>gnj2 n0 r0m0KtjIj2 2MI f (1 e )TDS•Acoustic pho<strong>non</strong>s peaks at Braggreflections•Optical and multipho<strong>non</strong> processeshave a smooth variationIn Debye modelITDSIhkl2MalnRgm Rhkl24 Jan 2006 Refresher course 5
Powder <strong>Diffraction</strong> - AdvantagesS<strong>in</strong>gle Crystal•Determ<strong>in</strong>e Crystal Structure•Fundamental physical propertiesPowder•Wider <strong>in</strong>vestigation ofphysical, chemical &mechanical properties•Easier to make <strong>in</strong> largequantity•Applications
Structure factorF N f exp[ 2i(hx ky lz )]exp[ M]KjjjjjjjMj 28u2sS<strong>in</strong>222usis the root-mean square thermal displacement1/24/2012 7Discussion meet<strong>in</strong>g on synchrotronutilization
Rietveld method- Calculate Intensityyci s L F (2 2) P Akkk2ikkyBackgroundbiAbsorption factorScale factorPreferred orientation functionStructure factorReflection profile functionLorentz, polarization, and multiplicity factor1/24/2012 8Discussion meet<strong>in</strong>g on synchrotronutilization
Nd 0.5 Sr 0.5 MnO 3Effect of reduc<strong>in</strong>g the particle size800 nm40 nm
The structure factor <strong>in</strong> the case of crystall<strong>in</strong>e materialsSG jfjexp( iG rj)S f exp[ i2( hxky lz)]Gjj1/24/2012 10Discussion meet<strong>in</strong>g on synchrotronutilization
In the absence of long range order -Non crystall<strong>in</strong>e solids – Glass, liquids….Short range orderRadial distribution function - paircorrelation function# of atoms <strong>in</strong> a spherical shell ofunit thickness at a distance r froma reference atom<strong>Diffraction</strong> diffuse <strong>in</strong> natureG(r) = 4πrρ o [ρ(r)/ρ o -1]ρ(r) and ρ 0 are the local andaverage atomic densities1/24/2012 11Discussion meet<strong>in</strong>g on synchrotronutilization
Reciprocal lattice vector G replaced by arbitrary scatter<strong>in</strong>g vectors, Δk=k’-kS( k) f mexp( ikrm)mISSmnfmfnexp[ ik(rm rn)]( I f f s<strong>in</strong> Kr ) /mnmnmnKrmn1/24/2012 12Discussion meet<strong>in</strong>g on synchrotronutilization
S (K) = I/Nf 2Liquid structure factorN - # of atoms, f – Atomic form factorRadial distribution function, g(r)g(r)112 2 r0dK[S(K)1]K s<strong>in</strong>Kr1/24/2012 13Discussion meet<strong>in</strong>g on synchrotronutilization
I(q)q = 4π s<strong>in</strong>θ/λÅ -1G(r) 2 / qmaxq0q[S(q)1]s<strong>in</strong>(qr)dq1/24/2012 14Discussion meet<strong>in</strong>g on synchrotronutilization
1/24/2012 15Discussion meet<strong>in</strong>g on synchrotronutilization
G(r) 2 / qmaxq0q[S(q)1]s<strong>in</strong>(qr)dqq max should be at least 20 Å -1 possible only with synchrotron or MoRemove air background, sample holder, correct for absorption effects, ifanyCorrect data for Compton scatter<strong>in</strong>g1/24/2012 16Discussion meet<strong>in</strong>g on synchrotronutilization
•RAD•PDFX•RMCPOW1/24/2012 17Discussion meet<strong>in</strong>g on synchrotronutilization
1/24/2012 18Discussion meet<strong>in</strong>g on synchrotronutilization
Neutron Scatter<strong>in</strong>g - Elemantary• Neutron <strong>in</strong>teracts with nuclei• It has a magnetic moment
Experimental facilities <strong>in</strong> Dhruva24 Jan 2006 Refresher course 20
The measure of the isotropic size effectsize(gaussian) 180 Z<strong>in</strong> Angstromssize(lorentzian)360 2YAnisotropic broaden<strong>in</strong>g of size – only lorentzian component is considered andvarious models are chosen through the parameter F24 Jan 2006 Refresher course 21