A semiconductor structure includes a plurality of stack structures overlying a substrate. Each stack structure includes a first chalcogenide material over a conductive material overlying the substrate, an electrode over the first chalcogenide material, a second chalcogenide material over the electrode, a liner on sidewalls of at least one of the first chalcogenide material or the second chalcogenide material, and a dielectric material over and in contact with sidewalls of the electrode and in contact with the liner. Related semiconductor devices and systems, methods of forming the semiconductor structure, semiconductor device, and systems, and methods of forming the liner in situ are disclosed.