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0Optical properties of LiNbi-xTaxO3 solid solution crystals
E.V. Zabelina1*, A.A. Mololkin1'2'3, N.S. Kozlova1, V.M. Kasimova1, R.R. Fakhrtdinov3, V.E. Umylin1, A.V. Sosunov4
1- National University of Science and Technology "MISIS", 119049, Russia, Moscow, Leninskypr., 4, b. 1 2- FOMOS-MATERIALS, 107023, Russia, Moscow, Buzheninova st., 16
3- Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, 142432, Russia, Moscow region, Chernogolovka, Academician Osipyan st., 2 4- Perm State University, 614990 Russia, Perm, Bukireva st., 15
LiNbO3 (LN) and LiTaO3 (LT) are well-known ferroelectric crystals that are widely used in the field of optics and acoustics to create electro-optics products, nonlinear optics, surface acoustic wave devices, piezoelectric sensors, etc. LN and LT are isomorphs, have a pseudo-ilmenite structure in the ferroelectric phase, belong to the 3m point symmetry group, and are described within the sp. gr. R3c.
In the ternary quasi-binary Li2O-Nb2O5-Ta2O5 system, a series of complex oxides may exist. The composition of these oxides vary, depending on the ratio of isomorphic cations. The lithium oxide concentration of 50% may result in the formation of a continuous series of LiNb(i-x)TaxO3 (LNT) solid solutions with different ratios of isomorphic cations (from LiNbO3 to LiTaO3). This makes it possible to obtain crystals of LNT solid solutions of intermediate compositions. Composition change makes it possible to significantly regulate the physical properties of the material and obtain crystals with different properties.
In this regard, the goal of this work was to obtain LNT crystals of intermediate compositions and study their optical properties.
LNT were grown at the Institute of Microelectronics Technology and High Purity Materials of the Russian Academy of Sciences by the Czochralski method in Pt crucibles using an upgraded NIKA-3M system [1].
The crystals were grown from a charge of two different compositions: LiNb0.95Ta0.05O3 and LiNb0.97Ta0.03O3. According to the phase diagram, crystals of the composition LiNb0.88Ta0.12O3 are grown from the charge LiNb0.95Ta0.05O3, and from the charge LiNb0.97Ta0.03O3 - crystals with composition LiNb0.93Ta0.07O3.
After the growth, the crystals were subjected to longterm annealings in the growth chamber at a temperature of 950-1100°C for 8-12 h.
From LiNb0.88Ta0.12O3 and LiNb0.93Ta0.07O3 crystals we prepared samples in the form of rectangular parallelepipeds with polished faces oriented along the crystallophysical axes in a standard setup. All samples were subjected to high-temperature electrodiffusion treatment (monodomenization) to bring the crystals to the single-domain state and eliminate the macro- and microdefect structure. The optical properties of the sample were investigated in the accredited tested laboratory of semiconductor materials and dielectrics "Single Crystals and Stock on their base" of National University of Science and Technology "MISIS". The spectral dependences ofthe transmittance T(^) were measured on a Cary-5000 spectrophotometer (Agilent Technologies) with a universal measurement accessory (UMA) in natural polarized visible light (300-700 nm).
This study was supported by the Ministry of Science and Higher Education of the Russian Federation within State assignment no. 075-00296-24-01 (in the part concerning the growth of experimental samples of LiNb1-xTaxO3 crystals) and within State assignment for Higher Education Institutions no. FSME-2023-0003 (in the part concerning the investigation of the optical properties of LiNb1-xTaxO3 crystals).
[1] D. Roshchupkin, R. Fakhrtdinov, B. Redkin, et al, Growth of ferroelectric lithium niobate-tantalate LiNb(i_x)TaxO3 crystal, Journal of
Crystal Growth, vol. 621. № 1, pp. 1-8, (2023).
