O3 Single Crystals Research Articles

Improving Strain in Single Crystal by Composition-Gradients Design

Domain switching is one of the essential contributions for strain in ferroelectric materials. In this work, we utilize anisotropic composition gradients (CGs) to induce anisotropic orientation of both defects and spontaneous dipoles, aiming to enhance the contribution of domain switching on strain in KTa1-xNbxO3 single crystal. In this way, a remarkable improvement (over 60%) of strain is obtained in KTa0.58Nb0.42O3 single crystal along the smallest CG direction, achieving a large unipolar strain, i.e. 0.29%, at low driving electric field 10 kV cm-1. It is attributed to the preferred orientation of both defects and spontaneous dipoles along the largest CG directions, then improving the contribution of domain switching on strain along the smallest CG direction. Particularly, owing to the existence of E>sub>in as recoverable forces caused by both flexoelectric fields and defects pinning effect, KTN show nearly zero remnant strain (srem) along the small CG directions, corresponding to the double P-E loops. Moreover, the V-PFM images confirm that CGs can influence the microdomain structures. Thus, designing special anisotropic CGs materials is expected to be a novel method to improve the strain properties and a potential way to flexibly design next-generation anisotropic piezoelectric materials.

Accurate determination of temperature dependent full matrix parameters of piezoelectric materials using only one sample

It is of great importance to accurately determine the full matrix parameters of the piezoelectric materials using as few samples as possible. Here we performed a simple and widely applicable method to accurately determine the full matrix parameters of [001]C-poled K(Ta,Nb)O3 single crystal. Only one sample was used throughout the experiment procedure, which eliminated inconsistency from multi-sample testing. We also improved the accuracy of results by inversing the impedance spectra of two inequivalent crystallographic directions, [001]C and [010]C. Based on this technique, variation of full matrix parameters with temperature were obtained using one sample. This work is of great significance for the characterization of novel piezoelectric materials and the evaluation of the performance of piezoelectric devices at various temperature.

Phase Transitions and Local Polarity above TC in a PbZr0.87Ti0.13O3 Single Crystal

Solid solutions of PbZr1−xTixO3 (PZT) are one of the most widely used piezoelectric materials with perovskite structure. Despite the decades of research, the phase diagram of PZT reported in 1971 has not been resolved yet. Recently, it turned out that single crystals of good quality of these solid solutions can be grown. By means of top-seeded solution growth (TSSG) technique, we succeeded to grow a single PbZr0.87Ti0.13O3 crystal. Hence, a partial verification of the diagram could be performed through investigations of the optical, dielectric, pyroelectric and elastic properties of this crystal, in a wide temperature range. The obtained results confirmed that the PbZr0.87Ti0.13O3 crystal undergoes a sequence of phase transitions, such as those observed in ceramics of similar chemical composition. However, additional anomalies of investigated physical properties were observed and discussed. Moreover, the influence of electric field on optical properties has been investigated for the first time and has proven the existence of local polar character of the phase above TC in a limited temperature range.

Para-ferroelectric phase transition driven by swift heavy-ion irradiation in KTN crystal

We report a novel approach of using swift O5+ ion irradiation to implement para-ferroelectric phase transition in a relaxor ferroelectric KTa0.62Nb0.38O3 (KTN) single crystal. With 15-MeV swift O5+ ion irradiation, a well-defined two-layer structure has been formed in the KTN sample due to the interaction between the O ions and KTN via electronic stopping and the nuclear stopping, respectively. The microstructures in these two layers are characterized by using a micro-Raman (μ-Raman) spectral technique. The significant changes of both spectral intensities and locations in three characteristic Raman peaks suggest that the top layer of the KTN sample due to electronic stopping exists a single-domain-ferroelectric state with a uniform and enhanced polarization orientation along [0 0 1]c direction. More importantly, we observe the irradiated region can effectively confine the light propagation in the ferroelectric layer, which can be further controlled by external fields. The results are promising for designing new integrated photonic devices.

Ultra-high piezoresponse in tantalum doped potassium sodium niobate single crystal

Ferroelectric materials reveal an ultra-high piezoelectric effect because of their spontaneous polarization and show high potential for applications. At present, the lead-free piezoelectric materials are in a great demand because of their environmentally friendly character, but their performance needs to be improved. Generally, in order to enhance the piezoelectric coefficients, researchers could rely on a phase boundary and/or to grow single crystals. Here, a Ta-doped (K, Na)NbO3 (KNN) single crystal with the orthorhombic–tetragonal (O–T) phase boundary is grown via the top-seed solution growth method. Excellent piezoelectric coefficients (d33 ≈ 560 pC/N via the Berlincourt method and d33* ≈ 1353 pm/V derived from strain-electric field loops) are achieved in a K0.40Na0.60Ta0.41Nb0.59O3 single crystal. What is more, with the electric field rising from 0.5 kV/cm to 4 kV/cm, the converse d33 and the strain hysteresis level improve from 580 pm/V to 640 pm/V and from 0.052 to 0.104, respectively. Our results clarify that the high d33 can be attributed to the high domain density and the labyrinthine-domain structure. In addition, the electric-field-induced phase transition is also observed, which is supposed to cause the high d33*. This work not only reports the ultra-high piezoresponse of the KNN-based single crystal but also provides strong evidence for its mesoscale origin.

Growth process of KTa0.65Nb0.35O3 single crystals and the influence of Cu-doping

Abstract KTN single crystals have some excellent optoelectronic properties and it’s been difficult to manufacture. This paper analyzes the applicable and suitable growth process parameters for KTN crystal, and the influence of Cu-doping on crystal structure and processibility. Large-sized and high-quality KTa0.65Nb0.35O3 crystals with different Cu-doping contents have been grown by the Czochralski method. The results reveal that lattice parameters increase slightly along with the increase of Cu-doping in KTN crystals. And 1.5 mol% of Cu doped KTN crystal has higher hardness, larger density and better thermostability than pure, 1 mol% and 3 mol% of Cu doped crystals due to its fine quality and no macroscopic defects during growth process.

T* of Relaxor Ferroelectric (1 − x) Pb(Zn1/3Nb2/3)O3‐xPbTiO3 Single Crystals Revisited Using Brillouin Spectroscopy

The relaxor characteristics of Pb[(Zn1/3Nb2/3)1–xTix]O3 (PZN‐xPT) single crystals (with x = 0 and x = 0.08) are investigated using temperature‐dependent Brillouin scattering spectroscopy. The longitudinal acoustic (LA) mode shows typical relaxor behaviors for PZN, whereas its mode frequency exhibits a discontinuous change at the phase transition temperature (TC) for PZN‐8%PT. The transverse acoustic (TA) mode, which is forbidden in an ideal cubic phase at the backscattering geometry, appears in both samples at a certain temperature above either the dielectric maximum temperature (Tm) or TC. This breakdown of the Brillouin selection rule in the cubic phase indicates that the noncubic polar regions become appreciable at this temperature where the interaction between the acoustic waves and the polar nanoregions (PNRs) is strong enough to enable the appearance of the TA mode. The intermediate characteristic temperature T* is determined in terms of the minimum of the temperature derivative of the half width of the LA mode, and the values are nearly the same as those determined via the acoustic emission signal measurements. These comparisons reveal the universal feature of the local phase transformation from dynamic to quasistatic PNRs at T*, giving rise to the appearance of the TA mode.

Czochralski growth and characterization of perovskite-type (La,Nd)(Lu,Sc)O3 single crystals with a pseudocubic lattice parameter of about 4.09 Å

Abstract (La,Nd)(Lu,Sc)O3 solid solution single crystals with liquidus temperatures of about 2170 °C were grown by the Czochralski method to provide perovskite substrates with a pseudocubic lattice parameter of 4.086 A for epitaxial purposes. We achieved single crystals with diameters up to 17 mm and total lengths up to 50 mm. Relatively high crystalline quality was confirmed by rocking curve measurements and by energy dispersive Laue mapping. Despite the complex composition, a good chemical homogeneity on the macroscale and nanoscale was verified by micro X-ray fluorescence elemental mapping and transmission electron microscopy. Only minor segregation along the pulling direction was found by chemical analyses using inductively coupled plasma atomic emission spectroscopy. Epitaxial La-doped BaSnO3 films grown on these substrates exhibited a mobility of 181 cm2 V−1 s−1 at room temperature.

Versatile power and energy conversion of magnetoelectric composite materials with high efficiency via electromechanical resonance

A better understanding of magnetoelectric (ME) energy materials with superior properties stimulates exploration of next generation of versatile energy devices with a high efficiency. Although a number of investigations have focused on developing multiferroic composite materials because of their potential in cutting-edge multifunctional devices, advances in basic research have not yet been translated into benefits for practical applications. In the present investigation, we introduce a two-phase magnetoelectric composite made of nanocrystalline FeBSi metallic ribbons (Metglas) and Mn3+,2+ acceptor doped Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PMN-PZT) single crystal, and great enhancements in ME coupling coefficient (αME~12500 V/Oe cm) with a tunable resonance frequency, current-to-voltage (I–V) conversion ratio (~15090 V/I), as well as power conversion efficiency (η ~95%) are found at the fundamental electromechanical resonance, which represent the highest values ever reported. This study also provides a fundamental understanding of the role of a figure of merit (FOM), kij,eff× Qm,eff, on ME coupling performances in ferromagnetic and ferroelectric two-phase ME composite. The enhanced performances are attributed to the laser heat treatment induced Nano crystallization in Metglas, lower magnetic and dielectric loss (tan δ), and also higher mechanical quality factor (Qm,eff) in ME composite. This research opens up the possibilities of developing ME composite materials for next-generation versatile energy and power conversion devices.

Thermodynamic characteristics of Li2MoO4, Li2W0.85Mo0.15O4 single crystals and stability direction for alkali molybdates

Single crystals of Li2MoO4 and Li2W0.85Mo0.15O4, as perspective materials to search for neutrino-less double beta decay, have been grown by low-temperature-gradient Czochralski technique (LTG CZ). The standard formation enthalpies for single crystals of Li2MoO4 and Li2W0.85Mo0.15O4 have been determined by two methods: (i) solution calorimetry in KOH (ΔfH0 (Li2MoO4, s, 298.15 K) = −(1521.9 ± 1.9) kJ mol−1) and (ii) high-temperature reaction calorimetry in sodium molybdate melt (3Na2O · 4MoO3) (ΔfH0 (Li2MoO4, s, 298.15 K) = −(1529.1 ± 7.3) kJ mol−1; ΔfH0 (Li2W0.85Mo0.15O4, s, 298.15 K) = −(1597.8 ± 4.3) kJ mol−1). The measured solution enthalpies of Li2CO3, MoO3, WO3, Li2MoO4, Li2W0.85Mo0.15O4 in 3Na2O · 4MoO3 melt and solution enthalpies of Li2CO3, MoO3, Li2MoO4 in KOH have been used to calculateΔfH0. The thermodynamic stability of A2MoO4 (A = Li, Na, K, Rb, Cs) with respect to simple oxides mixture has been determined. It has been found that the relative thermodynamic stability is increased from Li2MoO4 up to Cs2MoO4. This fact seems to be important from practical point of view. The lattice enthalpies for A2MoO4 compounds have been calculated using the Born-Haber cycle. The dependences of lattice enthalpies for A2MoO4 on structural parameters have been constructed, which allow one to predict the thermodynamics for compounds not investigated.

Effect of temperature on local structure of Pb(Zr0.58Ti0.42)O3 single crystal

We report the effect of temperature on the local structure of Pb(Zr0.58Ti0.42)O3 single crystal studied by X-Rays Absorption Spectroscopy (XAS) technique. The local structure related to Ti K-edge XANES reflects the significant change of the local structure of PZT unit cell before and after temperature variation. This change is likely caused by the shift of the Ti atom in the unit cell. More importantly, the clear agreement between the measured and calculated XANES spectra is supporting the evidence of local structure distortion in PZT material due to the small displacement of Ti atoms surrounded by oxygen atoms.

Spin reorientation and magnetocaloric effect of GdFe1-xMnxO3 (0 ≤ x ≤ 0.3) single crystals

In this paper, we have successfully synthesized the new single crystals of GdFe1-xMnxO3 (0 ≤ x ≤ 0.3), and investigated their spin reorientation and magnetocaloric effects. Compared with parent oxide GdFeO3, an additional spin reorientation transition from Γ4 to Γ1 is found in Mn-doped oxides with x = 0.2 and 0.3. The spin reorientation transition temperature, which is insensitive to the magnetic field even up to 10 kOe, can be tailored by changing Fe content. These findings are valuable for the design of magnetic switching devices. Moreover, the large values of magnetic entropy change at low temperatures suggest that GdFe0.7Mn0.3O3 single crystal is a promising candidate as the very low-temperature magnetic refrigerant.

High-Pressure Elastic Anomalies of PbHf0.975Sn0.025O3 Single Crystals Studied by Using Brillouin Spectroscopy

High-pressure Brillouin spectroscopy was applied to the PbHf0.975Sn0.025O3 single crystal to obtain the pressure dependences of its acoustic properties. The Brillouin frequency shift of the longitudinal acoustic mode showed two anomalies, one at ∼2.5 GPa and the other at ∼9 GPa, indicating two pressure-induced phase transitions consistent with recent Raman measurements. The half width of this mode exhibited damping anomalies at nearly the same pressures. The possible origin and the nature of these transitions are discussed.

Structure and properties of novel antiferroelectric PbHfO3-Pb(Mg1/2W1/2)O3 single crystals grown from high-temperature solution

Antiferroelectric (AFE) materials with perovskite structure have attracted great interest due to their distinctive structural complexity and useful physical properties. So far, most studies have focused on polycrystalline materials. Compared with the preparation of ceramics and films, the growth of Pb-based AFE single crystals with high quality is a more challenging task because of the high melting point, incongruently melting and the volatilization of Pb-containing components at high temperatures. In order to develop new antiferroelectric materials for energy storage applications and understanding the mechanisms of phase transitions and domain structure, single crystals of a new AFE-AFE solid solution of PbHfO3-Pb(Mg1/2W1/2)O3 (PHf-PMW) were successfully grown for the first time by the high-temperature solution growth method using the mixtures of PbO-B2O3 and Pb3O4-B2O3 as complex flux, respectively, and the grown crystals were characterized in terms of their crystal structure, dielectric properties and domain structure. It was found that Pb3O4 as the main flux component is more favorable than PbO as it lowers the melting point of the system and provides a more stable growth, leading to PHf-PMW crystals of larger size, better quality, higher optical transparency and less defects or inclusions. The structural analysis by XRD shows an orthorhombic Pbam symmetry at room temperature for the grown crystals, which is of antiferroelectric nature. By comparing the sequence and temperature of the phase transitions to the PHf-PMW ceramics, the compositions of the grown crystals are estimated to be 0.99PHf-0.01PMW and 0.985PHf-0.015PMW, respectively. Compositional segregation is observed in the grown crystals, which can be attributed to the incongruently melting character on the one hand, and the differences in the ionic radius and electronegativity of the oxygen anion and various B-site cations in the crystal lattice on the other hand. The observation and analysis of the ferroic domains by polarized light microscopy based on optical crystallography reveal domain structures consisting of two sets of domains with extinction directions parallel to the 〈110〉cub direction, confirming the orthorhombic symmetry. This work provides new experimental strategies in growing the high-quality antiferroelectric crystals of complex perovskite structure and a better understanding of their structure and properties for both fundamental studies and potential applications in optoelectronics and energy storage.

Study of the origin of the defects in La3Ga5.5Ta0.5O14 single crystals

We performed a comprehensive study of the properties of La3Ga5.5Ta0·5O14 crystals grown in different atmospheres before and after the post-growth treatments (annealing in air and vacuum) using different methods to clarify the origin of defects. The optical properties and elemental composition of the crystals depend on the growth atmosphere and the atmosphere of annealing. The absorption spectra of the colored crystals contain two strong broad bands in the UV spectral region (λmax∼290 and λmax ∼370 nm), one broad band in the visible range (λmax ∼480 nm). The spectra of the colorless crystals show a weak band at λmax ∼290 nm. The data obtained by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy indicate that there is a difference in the ratio of the main elements in dependence on the growth atmosphere and lack of gallium is observed at any growth atmosphere. An analysis of X-ray diffuse scattering indicates that the predominant type of defects is vacancy-type. There are more vacancy-type defects in crystals grown in Ar + O2 atmosphere than in Ar. On the base of the results of our study, we propose a self-consistent model of the defect origin in LGT crystals. The main defects are the Schottky-type defects. With add of oxygen in the growth atmosphere, F-centers are formed. During annealing in air, the concentration of the F-centers increases, and annealing in a vacuum leads to the destruction of F-centers.

Electrochemical stabilities of surface aluminum-doped LiNi0.5Co0.2Mn0.3O2 single crystals under different cutoff voltages

Surface Al-doped LiNi0.5Co0.2Mn0.3O2 (523) single crystals with a diameter of 2–4μm were synthesized by using Ni-Co-Mn hydroxide precursor and combined with further Al3+ coating/annealing operations. Al contents in the surface and the bulk structures of product particles were about 1.05% and 0.02%, respectively. XPS, XRD, and HRTEM results confirm that the Al element exist as a dopant within the layered structures of 523 surface. Coin cell testing of the as-prepared 523 cathode were taken under different voltage ranges of 3.0–4.3V, 3.0–4.4V, and 3.0–4.5V, with corresponding 100cycles capacity retentions of 91.2%, 74.0%, and 67.8% at 25°C, and 43.1%, 40.1%, and 31.6% at 55°C. The capacity degradation rate was mainly associated with the interfacial structure instabilities of 523 materials under different voltage ranges, which have been investigated by electrochemical impedance spectroscopy (EIS) and XPS.

Phase coexistence and broad depolarization response in (Pb,La)(Zr,Sn,Ti)O3 single crystals

Lead lanthanum zirconate stannate titanate (PLZST) antiferroelectric materials have been intensively studied in the last few decades due to their adjustable phase transition and outstanding performance. Despite the strong interest it has drawn, there is a lack of study of domain structure evolution in antiferroelectric materials with morphotropic phase boundary (MPB) composition, which is of great importance for understanding the phase transition between ferroelectric and antiferroelectric phase. PLZST single crystals with the composition in the MPB region were grown by the flux method in this work. We presented the direct evidence that rhombohedral ferroelectric and tetragonal antiferroelectric phase coexist in the as-grown single crystals. The evolution of phase structure and domain morphology during the temperature-induced phase transition was observed by in situ optical visualization, accompanied by a broadening depolarization response. An enhanced broadening pyroelectric response with a wide temperature window was detected. A modified Ginzburg-Landau-Devonshire theory was employed to elucidate the structural and physical origin of the broadening thermal depolarization. It is anticipated that a further understanding of the phase transition behavior in PLZST single crystals may be helpful in developing novel ferroelectrics and antiferroelectrics with MPB compositions.

Additional phase transition in a PbZr0.87Ti0.13O3 single crystal

PbZr1−xTixO3 (PZT) ceramics are one of the most known and widely used piezoelectric materials. In order to understand the origin of the high piezoelectricity it is essential to also understand its phase diagram. Many recent papers have reported the modification of PZT phase diagram based on ceramic experimental data. This is due to difficulties to get good quality single crystal samples. We have succeeded in getting a good quality single crystal with x = 0.13. Based on temperature changes of elastic properties we confirmed the existence of additional phase transition appearing in the PbZr0.87Ti0.13O3. The temperature dependence of the elastic properties was investigated by means of piezoelectric measurements and Brillouin light scattering. We discussed the correlation between anomalies of the elastic properties found in these measurements, and suggested that, except for the two well-known phase transitions, these anomalies point to another phase transition below Tc. The structure and symmetry of this crystal have been tested with use of the x-ray diffraction at the room temperature.

Vibrational properties of PbHf0.975Sn0.025O3 single crystal at high pressures

Antiferroelectric PbHf0.975Sn0.025O3 single crystals were studied at room temperature by Raman scattering at pressures up to 16 GPa using a diamond anvil cell. Two phase transitions were found to take place at pressures near 3 and 9 GPa, respectively, as revealed by subtle changes in Raman spectral features. A soft mode was observed at the pressure-induced phase transition occurring at 9 GPa. At pressures above ∼14 GPa, the Raman peaks become very weak and the background scattering becomes very strong. The characteristic parameters of the Raman structures were determined throughout the whole phase transitions sequence.

Synthesis of micron-sized LiNi0.5Mn1.5O4 single crystals through in situ microemulsion/coprecipitation and characterization of their electrochemical capabilities

LiNi0.5Mn1.5O4 single crystals are synthesized using a two-step method consisting of emulsion/in situ co-precipitation and sintering reaction. In this process, Oil-in-water (Span80-Tween80-kerosene-H2O) emulsion is used as the in situ co-precipitation site. The co-precipitation is occurred within each emulsion droplet to produce the precursor when the aqueous precipitant is dropped into the emulsion. For the starting concentration of the nickel and manganese solution determines the composition of each emulsion droplet, micrometer-sized single crystals of LiNi0.5Mn1.5O4 are finally produced based on the size and concentration of the emulsion droplet. Bigger crystals are helpful on the cyclic performance, whereas smaller crystals are effective on the specific capacity but negative on the cyclic performance. LNM-0.5 μm sized crystals deliver specific capacity of 136 mA g−1 at the 1st cycle and retain 129 mAh g−1 after 200 cycles, maintaining 95% of its initial capacity. However, LNM-0.25 nanoparticles deliver capacity of 119 mAh g−1 after 200 cycles and only maintain 89% of its initial capacity. At 20C rate, LNM-0.5 sample retains specific capacity of 111 mAh g−1 after 200 cycles, which is higher than that of LNM-0.25 sample with retention of only 90 mAh g−1. Based on the characterization and electrochemical measurement, it is observed that the LNM-0.5 sample with preferential crystal size presents excellent cyclic performance and rate performance.