A two-axis goniometer for sensitivity enhancement in single-crystal nuclear magnetic resonance spectroscopy

Abstract

The construction of a single-crystal nuclear magnetic resonance (NMR) probe with a new two-axis geometry for the goniometer has improved the sensitivity of the NMR response from small crystals. This allows studies of the smallest crystals used so far in single-crystal NMR. The goniometer of the probe uses only two different mountings of the crystal, and the rotation axis of the goniometer is tilted 45° with respect to the direction of the magnetic field. By moving the goniometer outside the radio frequency coil, the filling factor and the probe sensitivity increase. The improved sensitivity for the probe is illustrated by the P-{H1}31 cross-polarization spectrum of a 0.088 mm3 crystal of (NH4)2HPO4 and a Rb87 single-pulse spectrum of a 0.048 mm3 crystal of RbZn2(HPO4)PO4. Moreover, the capability to determine precise parameters for the solid-state NMR interactions using the new probe is demonstrated by Na23 and Rb87 single-crystal studies of NaNO3 and RbClO4.

A simple low-cost single-crystal NMR setup

“…As the precision of the parts printed by a 3D printer may be somewhat compromised compared to machined parts traditionally used in SC NMR probes [3][4][5][6][7][8][9][10][11][12], we expect that the mechanical design of the SC kit may be slightly skew compared to the drawings. For example, the motor axle may not be perfectly orthogonal to the magnetic field and the goniometer mounting may not be completely coaxial with the motor axle.…”

“…For example, the motor axle may not be perfectly orthogonal to the magnetic field and the goniometer mounting may not be completely coaxial with the motor axle. These deviations are not problematic as they can be handled in the data processing (vide infra), similarly to determining one of the goniometer angles through NMR experiments in our old two-axis SC NMR probe design [8]. While we can sacrifice the precision in the 3D printing, we fully rely on a reproducible setup, i.e.…”

“…This allows a full characterization of the magnitude and absolute orientation of the nuclear spin interaction tensors in the crystal frame. As the crystal needs be rotated stepwise in a controlled manner, dedicated SC NMR probes have been developed [3][4][5][6][7][8][9][10][11][12], which may seem sophisticated and cumbersome compared to conventional NMR probes due to the fact that the crystals have to be rotated precisely about at least two axes, thus demanding installation of mechanical facilities integrating with the NMR magnet and radiofrequency (rf) coil. The design of SC NMR probes needs to take into account that the head of even a wide-bore NMR probe is a compact space, the interior of the probe body is usually quite occupied and the installations sit tightly in a rigid scaffold, and that the main magnetic field additionally influences and limits the mechanical possibilities of an SC installation.…”

27Al-NMR/NQR Spectral Analysis of Single Crystal PrTa2Al20

“…First, according to several authors [8,9,10], we introduce three coordinates ΣL, ΣC, and ΣQ to deal with the situation. ΣL is a laboratory frame in which H0 is parallel to z-axis.…”

A two-axis goniometer for low-temperature nuclear magnetic resonance measurements on single crystals

“…From the practical point of view, a second rotation axis improves significantly the experimental efficiency, e.g., by avoiding interruptions of low-temperature experiments only for manually re-orienting the sample at room temperature. Despite its usefulness, the addition of a second rotation axis is generally considered as cumbersome due to constructional complexity 11 and, therefore, is often not pursued.…”