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Replication Data for: Decoding the AlPO₄ and LATP surface with a combined NMR-DFT approach

Supporting experimental and DFT data for the publication.

In the accompanying publication, we combine advanced nuclear magnetic resonance (NMR) experiments and density functional theory (DFT) simulations to study AlPO₄ as a model for the surface of the well-known solid ion conductor Li_1+xAl_xTi_2-x(PO₄)₃ with 0.3 ≤ x ≤ 0.5 (LATP), which is a promising candidate for the ceramic component of a hybrid electrolyte. By combining the multi-nuclei NMR techniques cross-polarization (CP) and transfer of populations in double resonance (TRAPDOR) on AlPO₄ powder with DFT calculations of NMR observables for a variety of surface models, the surface structure of commercial AlPO₄ is elucidated. It is shown that even after extended drying, the surface of AlPO₄ is hydroxylated with a TRAPDOR-estimated ¹H-²⁷Al quadrupolar coupling constant, C_Q, of 5.8 ± 0.9 MHz. The joint theoretical--experimental approach also enables first insights into the bonding motifs of organic entities on functionalized AlPO₄ surfaces as a model for the LATP surfaces, which confirm surface interactions and the presence of silane on both functionalized AlPO₄ and LATP. We demonstrate that observables, that are experimentally as well as theoretically accessible, provide information on interfacial bonding motifs, interatomic distances, and interactions, surpassing the capabilities of either NMR or DFT techniques alone.

The dataset contains the experimental NMR and EDX data as well as the atomistic structure models and the corresponding DFT simulations of NMR observables.
¹H, ⁶Li, ³¹P, and ²⁷Al NMR measurements were conducted on a Bruker Avance III HD spectrometer with a 9.4 T magnet. A 3.2 mm triple resonance H/X/Y CPMAS probe was used for all samples. All measurements took place with a probe temperature of 20 °C. The working frequencies were 400.2 MHz for ¹H, 58.9 MHz for ⁶Li, 162.0 MHz for ³¹P, and 104.3 MHz for ²⁷Al. No decoupling was used in the pulse sequence. The samples were measured at a spinning frequency of 20 kHz if not stated differently.
The EDX measurements were conducted on a Quanta FEG 650 scanning electron microscope (FEI), equipped with additional energy-dispersive X-ray spectroscopy equipment (SEM-EDX). An Everhard Thornley detector was used to detect the secondary electrons.
DFT calculations were conducted using the plane wave, pseudopotential electronic structure code CASTEP v.23. In this work, the C19 family of pseudopotentials was used that, in the case of Al and P, treats the 3s and 3p electrons explicitly. The Perdew-Burke-Ernzerhof (PBE) exchange correlation functional was employed for all the calculations. NMR observables were calculated with the GIPAW method as implemented in CASTEP v.23 with on-the-fly generated GIPAW pseudopotentials.
For further details, please refer to the related open source publication and Supplementary Information.

Please, switch to Tree View for the folder structure. The folder NMR contains the primary NMR data as Bruker files NMR/Bruker_files as well as the analyzed, secondary data NMR/Analysis in comma-separated CSV format, which is the basis for the figures in the related publication. The first line in the CSV files defines the parameter, the second the corresponding unit. NMR/Analysis/MAS_NMR_AlPO4_drying_series/Individual_fits_AlPO4_drying_series also includes the fitting parameters for the pseudo-Voigt fits of the ¹H and ²⁷Al NMR measurements of commercial AlPO₄ as well as dried AlPO₄ samples with different drying times. The first row represents the drying time and the corresponding errors, while the fitting parameters are specified in the first column. ³¹P MAS NMR spectra without CP were normalized by dividing the signal intensity by the respective absolute integral, while ²⁷Al MAS NMR spectra were normalized by dividing by the respective total integral and ¹H MAS NMR spectra were divided by the rotor content mass. ³¹P{¹H} CP spectra were normalized to the maximum intensity. The TRAPDOR raw data is provided with the frequency offset O2 as a file title, for example the file name "minus_2_0_MHz" corresponds to O2 = -2.0 MHz. The TRAPDOR pulse program was kindly provided by former colleagues of the authors from the Lab of Prof. Clare Grey. The following experiments are included

• MAS_NMR_AlPO4_drying_series ¹H, ³¹P, and ²⁷Al NMR measurements of commercial AlPO₄ as well as dried AlPO₄ samples with different drying times.
• MAS_31P_1H_CP_AlPO4_dried ³¹P{¹H} CP spectra with different contact times.
• TRAPDOR_27Al_1H_AlPO4_dried TRAPDOR spectra with different frequency offsets O2.
• MAS_1H_TMPES ¹H NMR spectrum of pure trimethoxy-(2-phenylethyl)silane (TMPES).
• MAS_1H_AlPO4_silanized ¹H MAS NMR spectrum of TMPES silanized dried AlPO₄.
• MAS_1H_LATP_silanized ¹H MAS NMR spectrum of TMPES silanized LATP.
• MAS_NMR_LATP/MAS_X_LATP where X specifies the nucleus; ⁶Li, ²⁷Al, and ³¹P MAS NMR spectra of LATP.

• AlPO4_bulk The different bulk phases of anhydrous AlPO₄ (berlinite, cristobalite, tridymite polymorphs) as well as AlPO₄ hydrates (variscite, UiO-7).
• AlPO4_surface The different surface models for berlinite AlPO₄ as well as the convergence test for the 001 slab.
• AlPO4_surfaceH2O The different hydrated and hydroxylated berlinite AlPO₄ surface models based on the buckled berlinite surface.
• AlPO4_TMPES The isolated TMPES molecule as well as the chemisorbed and physisorbed hydroxylated TMPES on top of the (P-OH)₂ surface of buckled berlinite AlPO₄.