With the development of the novel crucible material BaZrO3 in Geneva a new class of 123-single crystals has become available, the purities of which are now approaching semiconductor grade (>99.995%). Due to the exceptional purity, the experiments are no longer obscured by residual impurities and the influence of different oxygen content and distributions can be studied in detail. This has led to a set of new findings and a basic understanding of the physics of high Tc superconductivity. Examples of the impact of this new generation of crystals on the physics of 123-crystals are the reversible suppression of the so-called fishtail effect, which is accompanied by the absence of the Schottky anomaly in the low temperature specific heat and the calorimetric observation of the vortex lattice melting. On such samples it is possible to observe the vortex lattice by scanning tunneling microscope (STM) without any surface conditioning and to study the influence of pinning centers such as twin boundaries, micro-structural inhomogeneities of the metallic sub-lattice and oxygen vacancies on pinning of vortices.