Double helix dipole design applied to magnetic resonance: A novel NMR coil

International audienceA new radio frequency coil design for NMR experiments is presented. The coil generates a magnetic field purely perpendicular to the longitudinal axis of the main magnet, and its sensitivity is higher than the traditional transversal resonators. This is achieved by adding the contribution of two tilted solenoid coils fed with opposite currents. The work presents the mathematical model for the new coil, numerical simulations performed to validate that model and a comparison with an equivalent saddle coil. The new design is tested experimentally in low-and high-field NMR experiments and compared with results obtained with equivalent saddle coils. The results lead to conclude that the new design provides better sensitivity than the transverse resonators commonly used in NMR

Structures and Phase Transitions in (MoO2)2P2O7

We report structural investigations into (MoO2)2P2O7 using a combination of X-ray, neutron and electron diffraction, and solid-state NMR supported by first principles quantum chemical calculations. These reveal a series of phase transitions on cooling at temperatures of 377 and 325 K. The high temperature γ-phase has connectivity consistent with that proposed by Kierkegaard at room temperature (but with improved bond length distribution), and contains 13 unique atoms in space group Pnma with lattice parameters a = 12.6577(1) Å, b = 6.3095(1) Å, c = 10.4161(1) Å, and volume 831.87(1) Å3 from synchrotron data at 423 K. The low temperature α-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P21/c with cell parameters a = 17.8161(3) Å, b = 10.3672(1) Å, c = 17.8089(3) Å, β = 90.2009(2)°, and volume 3289.34(7) Å3 at 250 K. First principles calculations of 31P chemical shift and J couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D 31P solid-state NMR used to validate the proposed crystal structures. The intermediate β-phase is believed to adopt an incommensurately modulated structure; 31P NMR suggests a smooth structural evolution in this region