One valuable feature of this material is that both off-chain charge doping (Y3+Ca2+) and on-chain vacancy doping (Ni2+Zn2+, Mg2+) is possible [98,104,103]. Since charge-doping to the Haldane ground state is a unique feature, some previous measurements have been aimed to clarify the behavior of the doped charge.
DiTusa et al.  measured resistivity (), X-ray absorption spectroscopy (XAS), and inelastic neutron scattering (NIS) of the Ca/Zn-doped systems, and found the following features:
Quantitatively, vacancy doped Y2BaNiO5 has shown a mysterious response. Ramirez et al.  measured specific heat of the vacancy-doped compounds (Ni2+Zn2+) and found that the number of doping-induced spins does not follow the Valence Bond Solid state scenario; the VBS picture predicts the creation of two S=1/2 spins for each vacancy (see Fig.35d), but the Zn-doped Y2BaNiO5 system exhibited one S=1 spin for two Zn ions. To understand this phenomenon, Ramirez et al. suggest a heuristic `singlet-triplet model', which assumes that half of the broken chains form a triplet S=1 and the other half, a singlet S=0. Neither the origin of the couplings between the chain-end spins nor the local structure of the doping-induced spins is clear at the present stage.
To investigate the ground state properties and dynamics of spin systems, SR is a powerful technique as introduced in the previous chapter. The following presents SR results of the nominally pure/doped Y2BaNiO5, as well as their susceptibility data in low magnetic fields. For our measurements, polycrystalline specimens of nominally pure Y2BaNiO5, Ca doped systems [(Y2-xCax)BaNiO5; x=4.5, 9.5, 14.9 and 30.5%] and Mg doped systems [Y2Ba(Ni1-yMgy)O5; y=1.7 and 4.1%] were prepared at the University of Tokyo, Superconductivity Laboratory, using a standard solid state reaction described below :