LiNbO3 Structure Research Articles

Mechanisms of Variation of the Unipolarity during Thermal Processing of Heavily Doped LiNbO3:ZnO Crystals

The phenomenological mechanisms for increasing the unipolarity under thermal processing in the short-circuiting conditions for heavily doped LiNbO3:ZnO crystals are analyzed by comparing with the temperature behavior of nominally pure LiNbO3:ZnO crystals with the congruent composition. It is shown that an increase in the unipolarity and, hence, the disappearance of the domain structure in heavily doped LiNbO3:ZnO crystals is initiated by thermal decomposition of charged polar clusters stabilizing domain walls. The decomposition of polar clusters is accompanied with an abrupt jumpwise injection of extra charge carriers (Li+ cations). As a result, the conductivity of LiNbO3:ZnO crystals at a temperature above 800 K is an order of magnitude higher than that of nominally pure LiNbO3 crystals with the congruent composition. This leads to the degradation of the domain structure in LiNbO3:ZnO crystals in contrast to LiNbO3 crystals with the congruent composition.

FEATURES OF THE DEFECT STRUCTURE AND OPTICAL PROPERTIES OF AN LiNbO3:Mg(5.05):Fe(0.009 mol%) CRYSTAL

Defects and optical properties of LiNbO3:Mg(5.05):Fe(0.009 mol%) are studied by IR absorption spectroscopy, Raman spectroscopy, laser conoscopy, and optical spectroscopy. Absorption bands corresponding to OH stretching vibrations are shifted to higher frequencies and are narrower in the spectrum of this crystal than in the spectrum of a nominally pure congruent LiNbO3 crystal. This indicates that the OH groups are more ordered and the O–H bonds are more rigid in the structure of LiNbO3:Mg(5.05 ):Fe(0.009 mol%) than in the congruent crystal.

Synthesis, Elasticity, and Spin State of an Intermediate MgSiO3‐FeAlO3 Bridgmanite: Implications for Iron in Earth's Lower Mantle

AbstractFe‐Al‐bearing bridgmanite may be the dominant host for ferric iron in Earth's lower mantle. Here we report the synthesis of (Mg0.5Fe3+0.5)(Al0.5Si0.5)O3 bridgmanite (FA50) with the highest Fe3+‐Al3+ coupled substitution known to date. X‐ray diffraction measurements showed that at ambient conditions, the FA50 adopted the LiNbO3 structure. Upon compression at room temperature to 18 GPa, it transformed back into the bridgmanite structure, which remained stable up to 102 GPa and 2,600 K. Fitting Birch‐Murnaghan equation of state of FA50 bridgmanite yields V0 = 172.1(4) Å3, K0 = 229(4) GPa with K0′ = 4(fixed). The calculated bulk sound velocity of the FA50 bridgmanite is ~7.7% lower than MgSiO3 bridgmanite, mainly because the presence of ferric iron increases the unit‐cell mass by 15.5%. This difference likely represents the upper limit of sound velocity anomaly introduced by Fe3+‐Al3+ substitution. X‐ray emission and synchrotron Mössbauer spectroscopy measurements showed that after laser annealing, ~6% of Fe3+ cations exchanged with Al3+ and underwent the high‐ to low‐spin transition at 59 GPa. The low‐spin proportion of Fe3+ increased gradually with pressure and reached 17–31% at 80 GPa. Since the cation exchange and spin transition in this Fe3+‐Al3+‐enriched bridgmanite do not cause resolvable unit‐cell volume reduction, and the increase of low‐spin Fe3+ fraction with pressure occurs gradually, the spin transition would not produce a distinct seismic signature in the lower mantle. However, it may influence iron partitioning and isotopic fractionation, thus introducing chemical heterogeneity in the lower mantle.

Bidomain ferroelectric crystals: properties and prospects of application

Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are among the most important and most widely used materials of coherent and nonlinear optics, as well as acoustics. High degree of uniformity and reproducibility has become the foundation of technology for manufacturing high-quality crystals, absorbed by many suppliers around the world. However, the above areas do not limit the use of LiNbO3and LiTaO3due to their unique piezoelectric and ferroelectric properties. One promising application of crystals is the design of electromechanical transducers for precision sensors and actuators. In this respect, the high thermal stability of the piezoelectric and mechanical properties, the lack of hysteresis and creep make it possible to create electromechanical converters with wide operating temperature range, that is beyond the capability of commonly used ferroelectric ceramics. The main advantage of LiNbO3and LiTaO3over other single-crystal piezoelectrics is ferroelectric domain structure regulation toward targeted impact on the device characteristics. One of the most striking examples of electromechanical transducer design through domain engineering is the formation of a so-called bidomain ferroelectric structure in crystal. It represents a single-crystalline plate with two macrodomains with opposite directions of spontaneous polarization vectors separated by a charged domain wall. High switching fields make inversion domains stable at temperatures up to 1000 °C. This review summarizes the main achievements in the formation of bidomain structure and near surface inversion domains in LiNbO3and LiTaO3crystals. We present the domain structure virtualization methods in crystals and non-destructive methods for controlling the domain boundary position. The report contains a comparative analysis of the methods for forming inversion domains in crystals, and the patterns and technological control methods of the domain structure are discussed. The basic physical models have been proposed in the literature to explain the effect of the inversion domains formation. In the present paper we outline what one sees as strengths and weaknesses of these models. The strategies of crystallographic cut selection to create devices based on bidomain crystals are briefly discussed. We provide examples of the implementation of devices based on bidomain crystals such as actuators, sensors, acoustic transducers, and waste energy collection systems.

Cleavage and surface energies of LiNbO3

“Cleavage” is one of the most well-known modes of mechanical failure of crystals. It describes their ability to break easily along specifically oriented atomically sharp planes. Although understanding cleavage properties of any crystalline functional material is mandatory, the current knowledge about cleavage is limited to simplest crystals like cubic silicon. With the goal of expanding the knowledge to the broader class of crystalline materials, the cleavage of trigonal LiNbO3 single crystal is investigated in this work. The experimental method to measure the cleavage energy is introduced. The method is based on adhering a pre-cracked specimen in a rectangular hole in aluminum loading frame; forces are applied to the cracked specimen when heating up the assembly and due to the thermal expansion coefficient mismatch between the specimen and the loading frame. The cleavage energies of two known cleavage planes are evaluated by this method followed by extraction of the surface energies, and third previously unknown cleavage plane is discovered. The findings are explained qualitatively by counting the number of Nb–O bonds in LiNbO3 structure, broken by these planes. The evaluated fracture properties can be used to prevent catastrophic failure or for optimal design of the LiNbO3 crystal at service.

Power transmission characteristics of EWC-SPUDT SAW filters fabricated for multiplex transmission system of inverter gate drive circuits

To increase the electrical power transmission of surface acoustic wave (SAW) filters for gate drive systems of power conversion circuits, we fabricated unidirectional SAW filters based on a SiO2/Al/Pt/LiNbO3 structure in the frequency range of 380–950 MHz and measured their power durability characteristics. A transversal-type electrode-width-controlled single-phase unidirectional transducer (EWC-SPUDT) design was used to reduce the insertion loss of the SAW filters. Our experimental results showed that the transmitted electric power of the output port exceeded 560 mW, which was sufficient for the gate drive circuits. The results obtained demonstrate the validity of the SiO2/Al/Pt/LiNbO3 structure for the proposed EWC-SPUDT design.

Optical and Structural investigations of LiNbO3 thin films by PLD

Lithium niobate (LiNbO3) nanostructure thin film was prepared and deposited on the substrates made of quartz by utilizing pulse laser deposition (PLD) technique. The effect of substrate temperature changing on the optical and structural properties of LiNbO3 films was investigated and studied. The chemical mixture was prepared by mixing the raw material (Li2CO3, Nb2O5) with Ethanol liquid without any further purification, at the stirrer time 3hrs without heating, then the formed material was overexposed to annealing process at 1000°C for 4hrs. LiNbO3 nanostructure thin film was characterized and analyzed by utilizing the Ultra-Violet visible (UV-vis) and X-Ray Diffraction (XRD). The UV-vis results showed that the increase in the substrate temperature to 300°C leads to decrease in the values of transmission (T%), absorption (A) and optical energy gap (Eg) and increase in the values of reflection (R%) and refractive index (n). While, the XRD results explained that the LiNbO3 structure became more pure and crystalline with increase the substrate temperature, because the intensity of the phase 2θ at the value of 34.8°, 40.06° and 48.48° correspond to (110), (113) and (024) planes disappeared at the substrate temperature 300°C. So, all presented results give a good indication to use LiNbO3 nanostructure thin film prepared at the substrate temperature 300°C for manufacturing the optical waveguide to give the best results.

Correction: p-Type conductivity mechanism and defect structure of nitrogen-doped LiNbO3 from first-principles calculations.

Correction for 'p-Type conductivity mechanism and defect structure of nitrogen-doped LiNbO3 from first-principles calculations' by Weiwei Wang et al., Phys. Chem. Chem. Phys., 2020, 22, 20-27.

Исследование механизмов изменения степени униполярности при термической обработке сильно легированных кристаллов LiNbO-=SUB=-3-=/SUB=-:ZnO

Phenomenological mechanisms of an increase in unipolarity degree at thermal treatment under short circuit conditions of strongly doped crystals are researched by comparison with thermal behavior of nominally pure LiNbO3 crystals of congruent composition. It has been shown that an increase in unipolarity degree, and correspondingly vanishing of domain structure in strongly doped LiNbO3:ZnО crystals starts by thermal decomposition of charged polar clusters. These clusters stabilize domain walls. The decomposition is accompanied by sharp jump-like injection of additional charge carriers (Li+ cations). Due to this, conductivity of LiNbO3:ZnО crystals is one order of magnitude higher at temperature above 800K than in nominally pure LiNbO3 crystals of congruent composition. The injection leads to decomposition of domain structure in LiNbO3:ZnО crystals in spite of LiNbO3 crystals of congruent composition.

Comparative Study of Real Structure of LiNbO3 : ZnO Crystals Grown by Direct and Homogeneous Doping

A comparative study of the optical and structural homogeneity of a LiNbO3 crystal with a congruent composition and LiNbO3 : ZnО ([ZnО] ≈ 5.4–6.4 mol % in melt) crystals grown from charges of different origin has been performed. It is shown that the LiNbO3 : ZnО crystals obtained by direct solid-phase doping have a higher general structural and optical homogeneity, provided that the crystal composition is sufficiently homogeneous along the growth axis. Homogeneously doped LiNbO3 : ZnО crystals, characterized by a high general structural homogeneity on the scale level of 10–500 µm, have poorer optical and structural homogeneity on the micron and submicron levels as compared with directly doped LiNbO3 : ZnО crystals.

Effect of titanium in LiNbO3 on domain growth during e-beam writing

We report the features of domain growth during e-beam recording on non-polar Y-surfaces of LiNbO3 crystals doped with titanium at various concentrations (CTi). The nominally pure LiNbO3 of the congruent composition (CLN), LiNbO3 doped with 0.5 mol% TiO2 (CLN-0.5Ti), and the Ti:LiNbO3 planar waveguide formed as a result of high-temperature diffusion of titanium were comparatively studied. The titanium concentration at the surface of Ti: LiNbO3 was ∼7.6 at%, then CTi gradually decreased to 0.5–0.8 at% аt a depth of ∼4–5 μm. The combination of the etching technique with non-destructive methods of observation of the created domain structures of a planar type (low-voltage SEM and SHG microscopy) made it possible to detect the effect of titanium concentration on the features of the domain growth. It has revealed that the domain sizes and the average rate of their frontal growth (Vf) in CLN and CLN-0,5Ti are different. The observed differences are discussed in the framework of the current model of the intrinsic defect structure of LiNbO3. A peculiar three-dimensional structure of domain gratings in the Ti:LiNbO3 over the waveguide depth was found. The differences in the formation of the upper and lower parts of periodic gratings in Ti:LiNbO3 are explained by a significant increase in conductivity near the surface of the waveguide in comparison with deeper layers. The obtained results are useful to match the position and design of planar domain gratings in Ti:LiNbO3 optical waveguides on non-polar surfaces for better conversion efficiency of integrated nonlinear devices based on quasi-phase-matching.

Defect structure and holographic storage properties of LiNbO3:Zr:Fe:Cu crystals with various Li/Nb ratios

A series of LiNbO3:Zr:Fe:Cu single crystals with various Li/Nb ratios ranging from 0.946 to 1.38 were grown in air by the Czochralski method. Both X-ray powder diffraction and ultraviolet absorption spectra have been examined, and are discussed with regard to the defect structure of the as-grown crystals. In addition, the conventional two-wave coupling experiment has been conducted with 532 nm laser to reveal the holographic storage properties. The results have shown the macroscopic photorefractive properties to correspond well to the microscopic defect structure changing with the composition. More specifically, LiNbO3:Zr:Fe:Cu crystals possess at once relatively high sensitivity, fast response time and dynamic range comparable with that of LiNbO3:Zr:Fe crystals, and at the same time maintain high saturation diffraction efficiency (up to 68%) close to that of typical photorefractive LiNbO3:Fe crystals (70%), as such denoting their potential as prominent holographic storage media.

Optical properties and structure particularities of LiNbO3 crystals grown from a boron-doped melt

A series of LiNbO3:B crystals was grown from the melt doped by boron. It is shown that LiNbO3:B crystals possess an increased resistance to optical damage. We have found changes according to Raman spectra confirming the ordering of Li+, Nb5+ cations and vacancies along the polar axis. The chemical interactions were studied in the system Li2O–B2O3–Nb2O5. Boron cations are unable to incorporate into a cation sublattice of LiNbO3, but they change the physic-chemical structure of a melt. It contributes to an increased structure and optical uniformity of LiNbO3:B.

Theoretical prediction of piezoelectric property of new LiNbO3-type compound AlTlO3

ABSTRACTBy using systematic first-principles calculation, we found that AlTlO3 compound of LiNbO3 structure shows large piezoelectric constants e33 of 10.7 C/m2 and d33 of 56.7 pC/N. These piezoelectric constants are approximately six times larger than those of LiNbO3. AlTlO3 is predicted to be stabilized above 7 GPa. On the other hand, the calculated dielectric constant ε33 shows diverged behavior around 2 GPa. This result indicates that AlTlO3 can be quenchable. Decomposition of the predicted piezoelectric constant revealed that the large piezoelectricity of AlTlO3 originates from the Tl displacement in accordance with external perturbation, which drives the ferroelectric soft mode of the corresponding paraelectric phase. However, the energy difference between the ferroelectric and paraelectric phases was small, approximately 1 meV/f.u. These insights suggest that fluctuation between ferroelectric and paraelectric phases causes large piezoelectricity in AlTlO3.

High-Pressure Synthesis of Non-Stoichiometric Li x WO3 (0.5 ≤ x ≤ 1.0) with LiNbO3 Structure.

Compounds with the LiNbO3-type structure are important for a variety of applications, such as piezoelectric sensors, while recent attention has been paid to magnetic and electronic properties. However, all the materials reported are stoichiometric. This work reports on the high-pressure synthesis of lithium tungsten bronze LixWO3 with the LiNbO3-type structure, with a substantial non-stoichiometry (0.5 ≤ x ≤ 1). Li0.8WO3 exhibit a metallic conductivity. This phase is related to an ambient-pressure perovskite phase (0 ≤ x ≤ 0.5) by the octahedral tilting switching between a−a−a− and a+a+a+.

Structural Features, Physicochemical, and Optical Characteristics of Lithium Niobate Crystals Grown from Boron-Doped Melts

Chemical interactions in the Li2O−B2O3−Nb2O5 system, as well as certain features of crystallization of LiNbO3 crystals growing from melts containing nonmetal impurities, are considered. It is shown that boron changes the structure of the melt and has a significant impact on the structure and physical characteristics of LiNbO3 : В crystals, practically not entering the lithium niobate structure. Notable changes and certain features were found in the Raman spectra of grown LiNbO3 : В crystals, which indicates changing the sequence of the main cations and vacancies along a crystal polar axis and distortion of the oxygen octahedrons. Meanwhile, the distortion of the oxygen octahedrons is anisotropic. LiNbO3 : В crystals have a higher structural homogeneity than congruent crystals, and are close in the number of NbLi defects to a crystal with a stoichiometric composition, differing from it by a substantially less photorefraction effect.

Structure and Optical Properties Of LiNbO3:В Crystals Grown from Charges of Different Origins

It was shown that, without entering the structure of the crystal, boron can change the structure of the melt and have a significant effect on the fine features of the structure and the physical characteristics of lithium niobate crystals. Crystals grown from a charge doped with boron by the direct solid-phase method have a stronger photorefractive effect and a smaller forbidden band width than crystals grown from the re-extract doped homogeneously with boron at the niobium pentoxide extraction stage.

Evolution of the Domain Structure of LiNbO3:ZnO Crystals during High-Temperature Annealing

We have studied the evolution of the domain structure of LiNbO3:ZnO crystals during high-temperature annealing. The results demonstrate that the thermal decomposition of polar clusters that stabilize domain walls in LiNbO3:ZnO crystals initiates a jumplike carrier injection and an increase in electrical conductivity, leading to domain structure breakdown.

Domain formation on the nonpolar lithium niobate surfaces under electron-beam irradiation: A review

In this review, our recent results on the electron-beam domain writing (EBDW) on the nonpolar surfaces of LiNbO3 crystals of different compositions are presented. Under EB irradiation of the nonpolar surfaces, domains nucleated in irradiation points grow frontally along the polar [Formula: see text]-direction in a thin (of microns in thickness) surface layer; the driving force is the tangential component of space-charge fields induced by EB in irradiation points. This geometry of the experiment provides a possibility of three-dimensional (3D) characterization of domain patterns using the combination of atomic force microscopy (AFM) and second harmonic generation (SHG) confocal microscopy methods. The obtained results permitted us to relate the main characteristics of domain formation (the domain sizes and velocity [Formula: see text] of the frontal motion) to the irradiation conditions (the accelerating voltage [Formula: see text] of scanning electron microscopy (SEM), EB current [Formula: see text], the inserted charge [Formula: see text]). The domain depth [Formula: see text] is controlled by [Formula: see text] via the electron penetration depth; the domain length [Formula: see text] increases linearly with [Formula: see text] owing to the domain frontal growth by the viscous friction law. The electron emission coefficient [Formula: see text] affects the domain formation due to the fundamental dependence of [Formula: see text] on [Formula: see text]. In the framework of current approach to EB charging of insulators, the effect of an enhanced conductance on EBDW characteristics is analyzed. The difference between EBDW characteristics observed in varied LiNbO3 compositions is discussed in the framework of the intrinsic defect structure of LiNbO3. The obtained results extend the possibility of EBDW application to a wider range of crystals.

Water-soluble polymers as chelating agents for the deposition of Er3+/Yb3+:LiNbO3 waveguiding films

Compared to other oxide materials, the sol-gel deposition of an optically transparent LiNbO3 waveguiding film of sufficient thickness (approx. 1 μm) is complicated by the presence of a highly hydrolyzing Nb(V) in the starting solution. Thicker films require more concentrated solutions that are not easily achieved for such ions. This problem may be solved using strong chelating agents such as water-soluble polymers. To prepare a stable Er(III)/Yb(III)/Li(I)/Nb(V)/2-methoxyethanol solution with high metal concentration, we tested three such polymers: polyethylene glycol (PEG), polyacrylic acid (PAA) and polyvinyl alcohol (PVA), and compared them with already used polyvinylpyrrolidone (PVP). The solutions were spin-coated on crystalline sapphire substrates under a multi-step heating-deposition regime. Apart from Er3+/Yb3+ photoluminescence properties, we evaluated the influence of the film microstructure (SEM, AFM) on optical transparency and waveguiding ability in the UV/Vis/NIR region (transmission and m-line spectroscopy). Among the newly tested polymers, only PEG was able to prevent Nb(V) hydrolysis up to a maximum metal concentration of 0.6 mol/L. For PEG and PVP, the crystallization temperature of the deposited films (between 700 °C and 1000 °C) was compared. After further optimization of the heating-deposition process, we were able to prepare a transparent Er3+/Yb3+:LiNbO3 film thick enough to guide an optical signal in the NIR region. Thus, the use of PEG results is one of the very few non-hydrolytic sol-gel methods suitable for the preparation of not only luminescent, but also waveguiding Er3+/Yb3+:LiNbO3 structures.