The influence of composition on optical properties of ferroelectric potassium lithium niobate single crystals

Homogeneous crack-free Potassium Lithium Niobate (KLN) single crystals with different Li content were grown up by the TSSG technique. Lattice vibration spectra of these samples were investigated using Raman spectroscopy. The results showed that characteristic Raman spectra of the [NbO₆]⁷⁻ octahedral ions were strikingly influenced by the Li ions. Thus, the symmetric bend vibration mode ν₅ of the KLN sample with higher Li content was split into three Raman peaks, while the sample with lower Li content displayed a single peak, supporting that the bend vibration modes of the [NbO₆]⁷⁻ octahedrons were obviously perturbed by Li ions occupying C-sites. Enhanced Raman peak intensities of the KLN sample post-annealed at 900 °C for 24 h evidenced that content of defects in KLN crystal might be reduced. The transmittance spectra showed that the crystal with higher Li content had better transmittance intensity.     

Growth and characterisation of ferroelectric potassium lithium niobate crystals

Abstract

Potassium lithium niobate crystals have been grown by the resistance heating Czochralski technique. The optical transmission spectrum of the crystal has been determined. The results showed that the spectrum properties of potassium lithium niobate crystals grown from a melt with a higher Li₂O content are better than that of crystals grown from the melt with a lower Li₂O content. The crystals grown by this method have good quality and second harmonic generation properties. Frequency doubling results of a quasi cw-Ti:sapphire laser using crystal samples showed that potassium lithium niobate can be used to double the frequency of near infrared quasi cw-lasers in the 890–960 nm wavelength range.     

Growth of lithium doped silver niobate single crystals and their piezoelectric properties

Lithium doped silver niobate (Ag_1−xLi_xNbO₃, 0 < x < 0.1) is one of the candidate materials for lead-free piezoelectric materials. In this study, Ag_1−xLi_xNbO₃ single crystals were successfully grown by a slow cooling method. Crystal structure was assigned to perovskite-type orthorhombic (monoclinic) phase. Dielectric properties were measured as a function of temperature. As a result, with increasing lithium contents, the phase transition at around 60 °C was shifted to lower temperature while the phase transition at around 400 °C was shifted to higher temperature. On the basis of these peak shifts, the lithium contents in Ag_1−xLi_xNbO₃ single crystals were determined. Moreover, P–E hysteresis measurement revealed that pure silver niobate crystal was weak ferroelectrics with P_r of 0.095 μC/cm² while Ag_0.9Li_0.1NbO₃ (ALN10) crystal was normal ferroelectrics with P_r of 10.68 μC/cm². About this ALN10 crystal, polling treatment was performed and finally piezoelectric properties were measured. As a result, high electromechanical coupling coefficient k₃₁ over 70% was observed.     

Domain structure and electrical properties of Gd-and Tm-doped lithium niobate single crystals

We have grown lithium niobate single crystals doped with rare-earth elements (Gd and Tm) and have examined etch patterns on their surfaces by atomic force microscopy. The thermal stability of their regular domain structure has been assessed, and their anomalous electrical properties have been studied in the temperature range 300–380 K.     

Review: Review of electrooptic and ferroelectric properties of barium sodium niobate single crystals

Barium Sodium Niobate (BNN) belongs to tungsten bronze type Ferroelectric material. The non linear coefficients of BNN are twice that of LiNbO₃. Large single crystal of BNN is useful in frequency doubling applications because its conversion efficiency and resistance to optical damage are superior to LiNbO₃. Present review describes the preparative details, sturcture, ferroelectric and electro optic properties of BNN.     

Enhanced piezoelectric properties of potassium niobate single crystals with fine engineered domain configurations

Potassium niobate (KNbO₃) single crystals were grown by a top seed solution growth (TSSG) method. At first, the electric field was applied along [0 0 1]_c (cubic notification system) direction of KNbO₃ crystals to induce the engineered domain configurations into KNbO₃ crystals. Prior to domain engineering, the piezoelectric properties of [0 0 1]_c oriented KNbO₃ single-domain crystals were measured. These measured values were completely consistent with the calculated apparent d₃₁ and d₃₂. Finally, the engineered domain configurations were induced into KNbO₃ crystals. As a result, piezoelectric properties increased with decreasing domain sizes of the engineered domain configuration.     

掺镁铌酸钾锂晶体的生长与介电特性

首次用提拉法生长了K3Li2 Nb5O15∶Mg晶体 ,在 10～70 0K的温度范围内 ,研究了该晶体的c、a方向片的介电温度特性 ,测量了频率在 5× 10 2 ～ 5× 10 8Hz范围内介电常数的频率依赖关系。结果表明除了在 62 3K附近有铁电 -顺电相变以外 ,还在 80K左右存在铁电 -铁电相变 ,其介电弛豫频率约为2 5 0MHz左右。     

铌酸锂晶体的结构与性能关系研究

在实验测定的结晶学数据基础上，键价模型和化学键方法都被应用于定量或定性的研究铌酸锂晶体的物理性质，例如介电性质（包括折射指数n0和二阶非线性光学系数dij）、居里温度Te和自发极化率Ps。在前期工作中提出的Nb^5＋位依赖Li^＋位敏感的模型已成功地应用于铌酸锂晶体多种物理性质的研究。结果显示，其物理性质对晶体组成有强烈的依赖性。Nb^5＋位对于铌酸锂晶体的机械性质具有很强的影响；而Li^＋位也与晶体的介电性质密切相关．同时Li^＋位也是对＋1～＋5价不同掺杂剂敏感的晶格位置。     

铌酸锂晶体的结构与性能关系研究

在实验测定的结晶学数据基础上,键价模型和化学键方法都被应用于定量或定性的研究铌酸锂晶体的物理性质,例如介电性质(包括折射指数n0和二阶非线性光学系数dij)、居里温度Tc和自发极化率Ps.在前期工作中提出的Nb5+位依赖Li+位敏感的模型已成功地应用于铌酸锂晶体多种物理性质的研究.结果显示,其物理性质对晶体组成有强烈的依赖性.＃Nb5+位对于铌酸锂晶体的机械性质具有很强的影响;而Li+位也与晶体的介电性质密切相关,同时Li+位也是对+1～+5价不同掺杂剂敏感的晶格位置.     

Effect of stoichiometry on the thermal expansion coefficients of lithium niobate single crystals

The chemical analysis of LiNbO₃ single crystals, with different melt compositions (Li/Nb) _m =0·945, 1·0, 1·1 and 1·2, grown by slow cooling technique, reveals a remarkable difference in solid and melt compositions. The thermal expansion coefficients alonga andc axes, determined by using Newton’s ring experiment, are found to increase anisotropically with increase in (Li/Nb) _m ratio. The variation in thermal expansion coefficient with increase in the (Li/Nb) _m ratio is discussed in the light of defect chemistry i.e. the partial replacement of Li⁺ by excess Nb⁵⁺ creates additional cation vacancies to attain the electro-neutrality in the crystal.     

Systematic hardness studies on lithium niobate crystals

In view of discrepancies in the available information on the hardness of lithium niobate, a systematic study of the hardness has been carried out. Measurements have been made on two pure lithium niobate crystals with different growth origins, and a Fe-doped sample. The problem of load variation of hardness is examined in detail. The true hardness of LiNbO₃ is found to be 630 ± 30 kg/mm². The Fe-doped crystal has a larger hardness of 750 ± 50 kg/mm².     

EPR and optical absorption studies of Cr3+ doped lithium potassium sulphate single crystals

X-band electron paramagnetic resonance (EPR) studies of Cr³⁺ doped lithium potassium sulphate single crystals have been done at room temperature. The Cr³⁺ crystal field and spin Hamiltonian parameters have been evaluated by employing resonance line positions observed in the EPR spectra for different orientations of external magnetic field. The evaluated g, D and E values are: g_x = 2.0763 ± 0.0002, g_y = 1.9878 ± 0.0002, g_z = 1.8685 ± 0.0002 and D = 549 ± 2 × 10^?4 cm^?1, E = 183 ± 2 × 10^?4 cm^?1. Using EPR data the site symmetry of Cr³⁺ ion in the crystal is discussed. Cr³⁺ ion enters the lattice substitutionally replacing K⁺ site. The optical absorption study of the single crystal is also done in 195–925 nm wavelength range at room temperature. By correlating optical and EPR data the nature of bonding in the crystal is discussed. The calculated values of Racah parameters (B and C), crystal field parameter (D_q) and nephelauxetic parameters (h and k) are obtained as: B = 697, C = 3247, D_q = 2050 cm^?1, h = 1.146 and k = 0.21.     

Growth and optical properties of near-stoichiometric Fe-doped lithium niobate crystal

The Fe-doped near-stoichiometric lithium niobate (LiNbO₃) crystal has been grown by top seeded solution growth (TSSG) method from congruent melt doped with 0.01 wt.% Fe₂O₃ and 10.9 mol% K₂O. The intrinsic defects and Fe ions location in crystal are investigated on O–H vibration absorption peak position in infrared region and intrinsic absorption edge in UV–VIS region. The photorefractive properties of near-stoichiometric Fe/LiNbO₃ are measured by two-wave coupling method. Compared with congruent Fe/LiNbO₃ with the same Fe doping concentration, near-stoichiometric Fe/LiNbO₃ expresses a greatly improved response speed at the cost of a little decrease of diffraction efficiency.     

The optical properties of alkali nitrate single crystals

Absorption of non-polarized light by a uniaxial crystal has been studied. The degree of absorption polarization has been calculated as a function of the ratio of optical densities in the region of low and high absorbances. This function is proposed for analysis of the qualitative and quantitative characteristics of uniaxial crystal absorption spectra. Non-polarized light spectra of alkali nitrate single crystals, both pure and doped with thallium, have been studied. It is shown that the absorption band at 300 nm is due to two transitions, whose intensities depend on temperature in various ways. There is a weak band in a short wavelength range of the absorption spectrum of potassium nitrate crystal, whose intensity increases with thallium doping. The band parameters of alkali nitrate single crystals have been calculated. Low-energy transitions in the nitrate ion have been located.     

Surface dendrite in lithium niobate crystals

The growth of a surface dendrite of a complex nature has been observed in lithium niobate grown perpendicular to the c-axis. The dendrite limbs in different directions are described and a growth mechanism is suggested. It was found that a small volume of the melt in the crucible and a rapid rate of cooling do not favour the dendritic growth.     

A comparative study on the domain switching characteristics of near stoichiometric lithium niobate and lithium tantalate single crystals

For pure SLN and SLT crystals the coercive field measured from ferroelectric hysteresis loop was found to be independent of ramp rate. Decreased lithium concentration in pure SLN samples, the coercive field and internal field are strongly enhanced. Nb_Li antisites are the major contribution to the internal field. Coercive field depends strongly on the ramp rate in case of MgSLN and MgSLT samples, because of domain pinning. The coercive field is considerably reduced in Mg doped SLN and SLT compared to pure samples, indicating that the switching fields are strongly dependent on the nonstoichiometry of the crystals. The coercive field values were found to be constant under multiple cycling in case of Mg (1 mol%) doped SLN crystal. A strong correlation is found to exist between coercive field value and the Curie temperature.     

Electrical properties of manganese modified sodium potassium lithium niobate lead-free piezoelectric ceramics

Effects of MnO₂ doping on the microstructure, densification, dielectric, ferroelectric and piezoelectric properties of (Na_0.5K_0.5)_0.935Li_0.065NbO₃ (NKLN) lead-free piezoelectric ceramics were investigated. On the one hand, the addition of a small amount of MnO₂ has little effect on the crystalline structure, however, slightly promotes sintering and grain growth, and improves the uniformity of microstructure to a certain degree. On the other hand, MnO₂ doped NKLN ceramics show hard properties in piezoelectric activities, possessing decreased room-temperature dielectric constant, loss tangent and piezoelectric constants d ₃₃, and increased mechanical quality factors Q _m. The 1.2 mol% MnO₂ doped NKLN ceramics have a loss tangent of approximately 1%, a Q _m of ∼170 and a d ₃₃ of 150 pC/N. These effects were considered to come from the formation of oxygen vacancies and the multi-valence states of Mn ions.