def sulfide_type(structure):
    """
    Determines if a structure is a sulfide/polysulfide

    Args:
        structure (Structure): Input structure.

    Returns:
        (str) sulfide/polysulfide/sulfate
    """
    structure = structure.copy()
    structure.remove_oxidation_states()
    s = Element("S")
    comp = structure.composition
    if comp.is_element or s not in comp:
        return None

    finder = SpacegroupAnalyzer(structure, symprec=0.1)
    symm_structure = finder.get_symmetrized_structure()
    s_sites = [sites[0] for sites in symm_structure.equivalent_sites if
               sites[0].specie == s]

    def process_site(site):

        # in an exceptionally rare number of structures, the search
        # radius needs to be increased to find a neighbor atom
        search_radius = 4
        neighbors = []
        while len(neighbors) == 0:
            neighbors = structure.get_neighbors(site, search_radius)
            search_radius *= 2
            if search_radius > max(structure.lattice.abc)*2:
                break

        neighbors = sorted(neighbors, key=lambda n: n[1])
        nn, dist = neighbors[0]
        coord_elements = [site.specie for site, d in neighbors
                          if d < dist + 0.4][:4]
        avg_electroneg = np.mean([e.X for e in coord_elements])
        if avg_electroneg > s.X:
            return "sulfate"
        elif avg_electroneg == s.X and s in coord_elements:
            return "polysulfide"
        else:
            return "sulfide"

    types = set([process_site(site) for site in s_sites])
    if "sulfate" in types:
        return None
    elif "polysulfide" in types:
        return "polysulfide"
    else:
        return "sulfide"