Temperature depedent crystal strcture to study Ni-Ni dimerization in a one-dimensional PbCd2Ni6Te3O18

Recently one-dimensional (1D) spin-chain systems have attracted considerable attention due to the possibility of Haldane gap formation for an integer spin system. The compounds PbCd2Ni6Te3O18 (M = Cd and Mn), having quasi-1D chains of Ni2+ (S=1) and Mn2+ (S=5/2) in their crystal structure, exhibit remarkably interesting magnetic properties. The susceptibility reveals an antiferromagnetic ordering at 25.7 K for M = Cd and 86.0 K for M = Mn. Further, the heat capacity measurements also support the AFM magnetic ground state in both compounds. Interestingly, the susceptibility of M = Cd exhibits a broad maximum at 45 K, which is above TN=25.7 K, indicating the formation of Ni-Ni dimers. Recently we have investigated the magnetic behaviour of a polycrystalline sample of PbCd2Ni6Te3O18 (with Cd-114) using the WISH beam line (RB2210365) at 2 K and we find an AFM ordering with propagation vector (1/3 1/3 0) with the Ni-moments along the c-axis. What is missing is the information on the temperature dependent crystal structure, i.e., Ni-Ni bond lengths/angles of PbCd2Ni6Te3O18 to study the effect of Ni-Ni dimer formation. We therefore propose to investigate temperature dependence of the crystal structure of PbCd2Ni6Te3O18 using the high-resolution neutron powder diffractometer (HRPD).