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Zusammenfassung

We present a comprehensive study on PrCaFeO4 using macroscopic methods, neutron and x-ray diffraction, as well as inelastic neutron scattering. One polycrystalline and two single-crystal samples were investigated exhibiting structural phase transitions from a high-temperature tetragonal phase to an intermediate orthorhombic phase (space group Bmeb) at 510 degrees C (783 K). At approximately 240 K a second structural phase transition takes place into the space group Pccn where the tilt axis of the FeO6 octahedra changes from the [100] to the < 110 > directions. Due to strong diffuse scattering at high temperatures neutron powder diffraction can only safely state that T-N is above 330 K. PrCaFeO4 exhibits a magnetic spin-flop phase transition where the magnetic moments turn from the b axis to the c axis upon cooling. However, the transition temperatures and the width of this magnetic transition are strikingly different between the investigated samples, suggesting a strong influence from the real structure. Indeed, a significant difference in the oxygen content was deduced by single-crystal x-ray diffraction. The magnon dispersion was studied by inelastic neutron scattering revealing a nearest-neighbor interaction comparable to that in LaSrFeO4 but with smaller anisotropy gaps. A clear interlayer dispersion was observed resulting from the structural distortions and the relief of geometrical frustration due to the orthorhombic splitting.