Physico-Chemical nanomaterials science

Photoinduced centers in the single crystals of PbO-MoO3 system
Trubitsyn M.P., Volnianskii M.D., Bochkova TM., Bondar D.S. 
Solid state physics and optoelectronics dept, Oles Honchar Dnipro National University, prosp. Gagarina 72, Dnipro, 49010, Ukraine.
E-mail: trubitsyn_m@ua.fm

In the double oxide PbO-MoO3 system there are two crystals, which attract attention due to high acousto-optical parameters: PbMoO4 and Pb2MoO5. Lead molybdate PbMoO4 has the scheelite-type structure, belonging to the tetragonal space group I41/a (Z = 4) with the lattice parameters a=b=0.543 nm, c=1.210 nm. Double lead molybdate Pb2MoO5 is optically biaxial crystal. The lattice of Pb2MoO5 belongs to monoclinic system with a space symmetry group C 2/m (Z = 4), the lattice parameters are a=1.422 nm, b=0.578 nm, c=0.733 nm, α=γ=90° β=114.00°.
The PbMoO4 crystal structure contains molecular anionic groups MoO42- which exist as distorted tetrahedra with S4 point symmetry group. All Mo–O distances are equal to 0.177 nm. The Pb2MoO5 structure contains analogous isolated MoO42- complexes and infinite Pb–O zigzag-like chains along the z crystallographic direction. Every fifth oxygen atom in Pb2MoO5 lattice belongs to Pb–O chains, whereas all other oxygen atoms belong to MoO42- groups.
In the abstract we report the photoinduced optical and dielectric effects which are observed both in PbMoO4 and Pb2MoO5. Earlier, the photochromic effect in PbMoO4 was attributed to the cation recharge: Pb2+ + Mo6+ → Pb3+ + Mo5+ [1]. Studying dielectric properties of Pb2MoO5 crystal irradiated with UV light makes it possible to detect dielectric response of (MoO3)- complexes. Such centers arise when photoelectrons are trapped by molybdenum ions with oxygen vacancy VO in the nearest surroundings [2]. Presence of the similar nanometer sized structural complexes are assumed as the reason of optical absorption and slow dielectric relaxation observed in UV irradiated crystals of PbO-MoO3 system.

1.	Bochkova T.M., Volnyanskii M.D., Volnyanskii D.M., Shchetinkin V.S. Color centers in lead molybdate crystals // Phys.Sol.State.-2003.- 45. - P.235-237.
2.	Volnyanskaya I.P., Trubitsyn M.P., Volnyanskii D.M., Bondar D.S. Dielectric properties of the Pb2MoO5 crystals irradiated with UV light // Visnik Dniproovs’kogo universitetu. Seria Fizika,radioelektronika - 2017.-25, N 24.-P. 79-83.