Eu
1−xBa
xTi
1−yM
yO
3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu
2+/Eu
3+ and Ti
4+/Ti
3+ in EuTiO
3 and Eu
0.7Ba
0.3TiO
3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co
2+/Ni
2+ in Eu
0.7Ba
0.3TiO
3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti
3+ numbers and an increase in Eu
3+ numbers. On the other hand, Ba
2+ doping led to an increased lattice parameter due to its larger ionic size than Eu
2+, whereas the Co
2+/Ni
2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu
0.7Ba
0.3TiO
3 exhibited a clear ferroelectricity, which persisted in the Co
2+/Ni
2+ co-doped samples until the doping levels of
y = 0.05 and 0.10, respectively. Eu
0.7Ba
0.3TiO
3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co
2+/Ni
2+ turned the samples from antiferromagnetic to ferromagnetic with transition temperatures of 2.98 K and 2.72 K, respectively. The cause for such a transition could not be explained by the larger lattice volume, oxygen vacancies and mixed valences of Eu
2+/Eu
3+, which were proposed in previous works. Instead, it was more likely to arise from a large asymmetric distortion of the Eu–O polyhedron introduced by the aliovalent doping, which promotes the admixture of Eu 5d and 4f states.
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