The temperature evolution of NiO$_{6}$ octahedral tilts as a probe to study charge stripes in Ln$_{1:67}$Sr$_{0:33}$NiO$_{4}$ (Ln=La/Nd)

Nd$_{1:67}$Sr$_{0:33}$NiO$_{4}$ and La$_{1:67}$Sr$_{0:33}$NiO$_{4}$ exhibit long range ordered (LRO) charge stripes below Tco$\sim $240K. When the charge stripes are static and long-range ordered, they have been seen as superlattice Bragg peaks in single crystal neutron and x-ray diffraction. We used neutron atomic pair distribution function (NPDF) technique to investigate the possibility of existence of localized charges above Tco, where, the LRO of the stripes disappears. Rigid body type NiO$_{6}$ octahedral tilts were used as a probe to study the local and average structural response to charge order. The amplitude of rotation of the octahedral units was used to investigate the observed large apical oxygen thermal ellipsoids (anisotropic thermal displacement parameters) in the a-b crystal plane. We measured enhanced tilt amplitudes in the local structure, compared to the average. We will discuss the temperature dependence of the tilt amplitudes and of the correlation length of the local tilt order and explore the potential relationship to local stripe order.