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Hybrid organolead perovskites (HOP) have started to establish themselves in the field of photovoltaics, mainly due to their great optoelectronic properties and steadily improving solar cell efficiency. Study of the lattice dynamics is key in understanding the electron-phonon interactions at play, responsible for such properties. Here, we investigate, via neutron and Raman spectroscopies, the optical phonon spectrum of four different HOP single crystals: MAPbBr3, FAPbBr3, MAPbI3, and α-FAPbI3. Low temperature spectra reveal weakly dispersive optical phonons, at energies as low as 2-5 meV, which seem to be the origin of the limit of the charge carriers mobilities in these materials. The temperature dependence of our neutron spectra shows as well a significant anharmonic behaviour, resulting in optical phonon overdamping at temperatures as low as 80 K, questionning the validity of the quasi-particle picture for the low energy optical modes at room temperature where the solar cells operate.

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Abstract-This paper presents a magnetic bearing set developed to work in a flywheel energy storage system. The bearing set is composed of a Permanent Magnetic Bearing (PMB) and a Superconducting Magnetic Bearing (SMB). A new configuration of a PMB having Nd-Fe-B magnets rings and a back yoke is proposed and compared with an existing one. Finite Element Method (FEM) simulations were used to design two different PMB configurations. Measurements results of axial and radial forces were carried out in Zero Field Cooling (ZFC) and Field Cooling (FC) processes. These measured force results are presented and discussed in order to discover which configuration is more promising for the proposed application.

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