  We investigate the structural and magnetic phase transitions in EuTi1-xNbxO3
with synchrotron powder X-ray diffraction (XRD), resonant ultrasound
spectroscopy (RUS), and magnetization measurements. Upon Nb-doping, the Pm-3m
to I4/mcm structural transition shifts to higher temperatures and the room
temperature lattice parameter increases while the magnitude of the octahedral
tilting decreases. In addition, Nb substitution for Ti destabilizes the
antiferromagnetic ground state of the parent compound and long range
ferromagnetic order is observed in the samples containing more than 10% Nb. The
structural transition in pure and doped compounds is marked by a step-like
softening of the elastic moduli in a narrow temperature interval near TS, which
resembles that of SrTiO3 and can be adequately modeled using the Landau free
energy model employing the same coupling between strain and octahedral tilting
order parameter as previously used to model SrTiO3.
