trioxide reported in the literature, the α- and γ- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of , and . Tellurium also exhibits mixed-valence oxides, and . The tellurium oxides and hydrated oxides form a series of acids, including tellurous acid (), orthotelluric acid () and metatelluric acid (). The two forms of telluric acid form tellurate salts containing the TeO and TeO anions, respectively. Tellurous acid forms tellurite salts containing the anion TeO. Zintl cations When tellurium is treated with concentrated sulfuric acid, the result is a red solution of the Zintl ion, . The oxidation of tellurium by in liquid produces the same square planar cation, in addition to the trigonal prismatic, yellow-orange : Other tellurium Zintl cations include the polymeric and the blue-black , consisting of two fused 5-membered tellurium rings. The latter cation is formed by the reaction of tellurium with tungsten hexachloride: Interchalcogen cations also exist, such as (distorted cubic geometry) and . These are formed by oxidizing mixtures of tellurium and selenium with or . Organotellurium compounds Tellurium does not readily form analogues of alcohols and thiols, with the functional group –TeH, that are called tellurols. The –TeH functional group is also attributed using the prefix tellanyl-. Like H2Te, these species are unstable with respect to loss of hydrogen. Telluraethers (R–Te–R) are more stable, as are telluroxides. Tritelluride quantum materials Recently, physicists and materials scientists have been discovering unusual quantum properties associated with layered compounds composed of tellurium that's combined with certain rare-earth elements, as well as yttrium (Y). These novel materials have the general formula of R Te3, where "R " represents a rare-earth lanthanide (or Y), with the full family consisting of R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er & Tm (not yet observed are compounds containing Pm, Eu, Yb & Lu). These materials have a two-dimensional character within an orthorhombic crystal structure, with slabs of R Te separated by sheets of pure Te. It's thought that this 2-D layered structure is what leads to a number of interesting quantum features, such as charge-density waves, high carrier mobility, superconductivity under specific conditions, and other peculiar properties whose natures are only now emerging. For example, in 2022, a small group of physicists at Boston College in Massachusetts led an international team that used optical methods to