  We combine structural and magnetic measurements to compare the different
magnetic phase diagrams between the pressure and substitution studies in
CeTiGe3. We report on the structural, magnetic, and electrical transport
properties of single crystals of CeTi1-xVxGe3 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.9,
and 1), and of polycrystalline samples (x = 0.5, 0.6, 0.7, 0.8), as well as
structural properties of CeTiGe3 under pressure up to 9 GPa. The ferromagnetic
ordering in CeTiGe3 is suppressed with V doping in CeTi1-xVxGe3, and suggests a
possible ferromagnetic quantum critical point near x = 0.45. We perform a
detailed crystalline electric field (CEF) analysis, and the magnetic
susceptibility data in pure CeTiGe3 and CeVGe3 can be well explained by the CEF
model. The proposed CEF energy levels suggest that there is a gradual change of
the ground state from 5/2 state in CeTiGe3 to 1/2 state in CeVGe3, and a
suppression of CEF splitting energies near the quantum critical region. When
hydrostatic pressure is used instead of chemical substitution, the quantum
critical point is avoided by the appearance of magnetic phases above around 4.1
GPa. In the substitution study, the ferromagnetic and antiferromagnetic regions
are well separated, whereas they touch in the pressure study. We observe a
different trend in the temperature dependence of the resistivity maximum in
both studies, suggesting that the CEF splitting energy is suppressed by V
substitution but enhanced by pressure. We also observe different responses in
lattice constants between the two studies, highlighting the fact that
substitution effects cannot be reduced to chemical pressure effects only.
Nevertheless, when the magnetic phase diagrams of both hydrostatic pressure and
substitution are compared, we find a common critical lattice constant c = 5.78
A where the ferromagnetic ordering is suppressed in both studies.
