Local Electronic Structure in AlN Studied by Single-Crystal 27Al and 14N NMR and DFT Calculations

Abstract

Both the chemical shift and quadrupole coupling tensors for 14 N and 27 Al in the wurtzite structure of aluminum nitride have been determined to high precision by single-crystal NMR spectroscopy. A homoepitaxially grown AlN single crystal with known morphology was used, which allowed for optical alignment of the crystal on the goniometer axis. From the analysis of the rotation patterns of 14 N ( I = 1 ) and 27 Al ( I = 5 / 2 ), the quadrupolar coupling constants were determined to χ ( 14 N ) = ( 8.19 ± 0.02 ) kHz, and χ ( 27 Al ) = ( 1.914 ± 0.001 ) MHz. The chemical shift parameters obtained from the data fit were δ i s o = − ( 292.6 ± 0.6 ) ppm and δ Δ = − ( 1.9 ± 1.1 ) ppm for 14 N, and (after correcting for the second-order quadrupolar shift) δ i s o = ( 113.6 ± 0.3 ) ppm and δ Δ = ( 12.7 ± 0.6 ) ppm for 27 Al. DFT calculations of the NMR parameters for non-optimized crystal geometries of AlN generally did not match the experimental values, whereas optimized geometries came close for 27 Al with χ ¯ calc = ( 1.791 ± 0.003 ) MHz, but not for 14 N with χ ¯ calc = − ( 19.5 ± 3.3 ) kHz.

Reactions of metal chlorides with hexamethyldisilazane: Novel precursors to aluminum nitride and beyond

“…After heating to 1600 • C/4 h/N 2 , a large peak at 114 ppm occurs, indicating AlN. [54][55][56] Another peak at 14 ppm suggests [AlO 6 ] units, but with different [AlO 6 ] peak positions and narrower when compared to Al-HMDS heated to 80 • and 800 • C. This suggests that the Al environment is more symmetrical for Al-HMDS heated to 1600 • C, likely a result of increased crystallinity, consistent with XRD in Figure 4A. EDX analysis suggests ∼15 at.% Cl content for the asdried Al-HMDS precursor, corresponding to -Cl inclusion indicated by MALDI (Figure 1).…”

Single-Crystal 31P and 7Li NMR of the Ionic Conductor LiH2PO4

“…a Drawing generated with the Vesta program [11]. Transformation of the CS tensor from the CRY frame to the PAS frame changes δ to diagonal form, with the eigenvalues δ 11 , δ 22 , and δ 33 placed on the main diagonal. The weighted trace of δ determines the isotropic chemical shift δ iso = 1/3(δ 11 + δ 22 + δ 33 ), with the asymmetry parameter of the CS tensor defined by η CS = (δ 22 − δ 11 )/∆δ.…”

“…For 7 Li with spin I = 3/2, the quadrupolar coupling between the non-symmetric charge distribution of the nucleus and its electronic surroundings also needs to be considered [20]. The number of energy levels for a spin I in an external magnetic field is 2I + 1, resulting in 2I NMR transitions, which are classified according to their magnetic quantum number m. With a particular transition |m → |m + 1 designated by the parameter k = m + 1 2 [21,22], the resonance frequency ν m,m+1 of this transition may then be described by adding the contribution of the quadrupolar interaction to Equation (1):…”

Editorial for the Special Issue on Solid-State NMR Spectroscopy in Materials Chemistry

“…In this Special Issue, Sorte et al [6] report a study of several Mg-based minerals by combining DFT calculations of 1 H chemical shifts with results from advanced 1 H NMR experimentation using dipolar interactions (see below). Moreover, Zeman et al [1] present DFT calculations of 27 Al and 14 N NMR parameters of AlN.…”

“…NMR on single crystals normally offers the most accurate NMR parameters. Zeman et al [ 1 ] present such a single-crystal 27 Al and 14 N NMR study of aluminium nitride, from which valuable parameters relating to the electronic structure were extracted. Yet, such single-crystal NMR studies are nowadays rare: solid-state NMR experiments are merely conducted directly on powders of micrometer-sized particles under so-called magic-angle spinning (MAS) conditions, where the powder is spun at a tens-of-kHz rate.…”