have attracted much attention due to their important applications as photoluminescent materials [1-3], microwave applications [4, 5], sensors , optical devices , photocatalysts , supercapacitors [9, 10] and others [11, 12].
(1) Low-temperature sulfur incrustations from Ebeko volcano contain appreciable amounts of trace elements stored in rock particles, metal sulfides (e.g., argentite ([Ag.sub.2]S), covellite (CuS), cadmoindite (Cd[In.sub.2][S.sub.4]), famatinite ([Cu.sub.3]Sb[S.sub.4])), chlorides (cotunnite (Pb[Cl.sub.2])), sulfates (anhydrite (CaS[O.sub.4]), alunite [(K[Al.sub.3](S[O.sub.4]).sub.2][(OH).sub.6]), anglesite (PbS[O.sub.4]), barite (BaS[O.sub.4])), and tungstates
Klevtsov, "A correlation between the structure and some physical properties of binary molybdates (Tungstates
) of uni- and bivalent metals," Journal of Structural Chemistry, vol.
Although several compounds have been reported to act as good corrosion inhibitors for steel in neutral media (e.g., molybdates, tungstates
, polyphosphate, and phosphonate) [1-5], the use of carboxylic acid derivatives has been attractive since they are environmentally friendly and can be derived from fatty acids extracted from vegetable oils [6, 7].
Nitrates, molybdates, and tungstates
also have been used.
The crystalline mineral matter typically comprised of oxides-hydroxides, sulphides-sulphosalts, sulphates, silicates, carbonates, phosphates, vanadates, tungstates
, chlorides, native elements, and other mineral classes (Ural, 2007; Vassilev and Vassileva, 1996).
 have carried out detailed study on thermal expansion of some other molybdates and tungstates
such as [Gd.sub.2][Mo.sub.3][O.sub.12] and [Gd.sub.2][W.sub.3][O.sub.12].
Pollnau, "Integrated lasers in crystalline double tungstates
with focusedion-beam nanostructured photonic cavities," Laser Physics Letters, vol.
Mihokova et al., "Excitonic emission of scheelite tungstates
AW[O.sub.4] (A = Pb, Ca, Ba, Sr)," Journal of Luminescence, vol.
Fuks, "New cadmium and rare earth metal tungstates
with the scheelite type structure," Journal of Rare Earths, vol.
Nevertheless, the so-called 'one-component' materials - such as manganese antiperovskites, zirconium vanadates, and hafnium tungstates
- exhibiting negligible thermal expansion offer a promising route towards achieving this goal.
The oxidizing agents can be peroxides, superoxides, permanganates, tungstates
, or molybdates.