O3 Single Crystals Research Articles

X‐Ray Diffraction and Dielectric Investigations of Ferroelectric PbZr0.958Ti0.042O3, Antiferroelectric PbZrO3 and PbHfO3 Single Crystals in Superstrong Electric Fields up to 30 MV/m

AbstractFerroelectric rhombohedral phase (R3m) in PbZr0.958Ti0.042O3 and antiferroelectric orthorhombic phase (Pbam) in PbZrO3 and PbHfO3 are examined via X‐ray diffraction and dielectric methods in DC electric fields of 0 ≤ Е ≤ 3.0⋅107 V/m. Induced polarization Pi(E) and piezoelectric coefficient d33(Е) are found as functions of field from the experimental dependences of unit‐cell parameters and dielectric permittivity on the electric field E and exhibit similar behavior for BaTiO3 and PbZr0.958Ti0.042O3 single crystals. The unit‐cell parameters of antiferroelectric phases in PbZrO3 and PbHfO3 single crystals remain constant, while the electric fields correspond to induced phase transitions, and the dielectric permittivity slightly increases with the electric field.

Flexible control of positive and negative electrocaloric effects under multiple fields for a giant improvement of cooling capacity

This paper demonstrated the flexible control of positive and negative electrocaloric effects (ECEs) in ⟨001⟩-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 single crystal, and a dual cooling cycle is proposed using their combination to improve cooling capacity. The ECE exhibits a complex evolution of positive-negative-positive within 20–140 °C, where the negative ECE originates from the electric field-induced transition from rhombohedral phase to high-symmetric tetragonal phase. Since the coexistence of different ECEs at some temperatures, the positive and negative ECEs alternately appear in neighboring cycles under proper applied fields, i.e., dual cooling. A significant improvement of ∼150% in cooling capacity is directly characterized by the isothermal heat flow measurement.

Temperature and field induced spin reorientation and dielectric properties in YCr0.88Fe0.12O3 single crystal

The structural, magnetic, and dielectric properties of the YCr0.88Fe0.12O3 single crystals were studied. Detailed magnetic studies demonstrate that the crystal is antiferromagnetic with weak canted ferromagnetism and experiences three sequential magnetic transitions around TN1 ∼ 127.3 K, TN2 ∼ 115.2 K, and TSR ∼ 99.0 K. Interestingly, a temperature induced spin reorientation (SR) near TSR and magnetic field induced SR below TSR were observed. The H–T phase diagram was revealed to be quite different from both parent compounds YFeO3 and YCrO3. A dielectric relaxation around TN1 was found to be associated with electron hopping. An intrinsic magnetoelectric effect was also observed at low temperatures. These results are helpful for understanding the exotic magnetic and magnetoelectric properties in the orthochromite and orthoferrite related systems.

Doping effects on the relaxation of frustration and magnetic properties of YMn0.9Cu0.1O3

The crystal structure and magnetic properties of hexagonal YMn0.9Cu0.1O3 single crystal are systematically investigated. The refinement results of XRD show the lattice constant decreases, which is unusually due to the doped Cu2+ ion has a larger ionic radius than the Mn3+ ions. The XPS results show that the coexistence of Mn2+, Mn3+ and Mn4+ ions in YMn0.9Cu0.1O3 single crystal. Magnetization measurements show that Cu doped YMn0.9Cu0.1O3 and parent YMnO3 have almost the same antiferromagnetic transition temperature TN, which indicates the AFM interaction is robust in the geometry frustrated system. Because doping directly destroy some of the Mn3+ ions nets, the relaxation of frustration of Mn in-plane 2D triangular geometry network leads to the significantly decrease of Mn3+ ions AFM interaction. In addition, the coexistence and competition between the ferromagnetic and antiferromagnetic interactions among the Mn2+, Mn3+ and Mn4+ ions lead to a complicated and irreversible magnetization behavior in YMn0.9Cu0.1O3 single crystal.

Dielectric and conductivity behavior of Mn-doped K0.5Na0.5NbO3 single crystal

Dielectric and conduction behaviors of [001]-oriented K0.5Na0.5Nb0.5O3 single crystal (KNN) and 0.5at% Mn-doped KNN single crystal (KNN-Mn) have been investigated in a broad temperature range. At low temperatures (330–400K), an observed slight decrease of conductivity could be connected with the decreases of hole carrier concentration and mobility for the KNN-Mn. At high temperatures (723–773K) above Cure temperature, the dielectric relaxation and conduction behavior of the samples were analyzed by measurements of impedance spectroscopy and universal dielectric response law. The activation energy values for relaxation frequency and conduction were ~ 0.97eV and 0.60eV for the KNN-Mn, respectively. They could be attributed to the thermal motion of double ionized oxygen vacancies and the formation of defect dipoles. The defect compensation mechanism was proposed based on Mn4+ ion substitution. The KNN-Mn promoted a higher concentration of oxygen vacancies compared with KNN crystal, which gave rise to smaller domain size and higher piezoelectric properties.

Electric field induced critical points and field gradient by trapped electrons in Li-doped KTa1-xNbxO3 single crystals

The effects of electric field and trapped electrons on a ferroelectric phase transition of the 5%Li-doped KTa0.74Nb0.26O3 crystals were investigated by micro-Brillouin scattering and dielectric measurements. In micro-Brillouin scattering, the remarkable changes of the central peak (CP) intensity were observed at the paraelectric cubic to ferroelectric tetragonal phase transition. The critical electric fields to induce the paraelectric to ferroelectric phase transition were found to shift to higher values with increasing temperature. From these CP results, we estimated lines of critical points for phase transitions including critical end point (CEP), (E, T) = (1.6 kV/cm, TC-T+3.4 °C) in the composition-temperature-electric field (x-T-E) phase diagram. The clear difference of the CEP was observed between Brillouin result at a fixed small area and dielectric result averaged over all area of a sample. It can be caused by the field gradient, which is induced by the trapped electrons. The existence of gradient of electric field was also discussed using the observed result of position dependence of the CP intensity.

Strain-Mediated Coexistence of Volatile and Nonvolatile Converse Magnetoelectric Effects in Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Heterostructure.

Strain-mediated ferromagnetic/ferroelectric (FE) heterostructures have played an important role in multiferroic materials to investigate the electric-field control of magnetism in the past decade, due to their excellent performances, such as room-temperature operation and large magnetoelectric (ME) coupling effect. Because of the different FE-switching-originated strain behaviors and varied interfacial coupling effect, both loop-like (nonvolatile) and butterfly-like (volatile) converse ME effects have been reported. Here, we investigate the electric-field control of magnetism in a multiferroic heterostructure composed of a polycrystalline Fe thin film and a Pb(Mg1/3Nb2/3)0.7Ti0.3O3 single crystal, and the experimental results exhibit complex behaviors, suggesting the coexistence of volatile and nonvolatile converse ME effects. By separating the symmetrical and antisymmetrical parts of the electrical modulation of magnetization, we distinguished the loop-like hysteresis and butterfly-like magnetization changes tuned by electric fields, corresponding to the strain effects related to the FE 109° switching and 71/180° switching, respectively. Further magnetic-field-dependent as well as angular-dependent investigation of the converse ME effect confirmed the strain-mediated magnetism involving competition among the Zeeman energy, magnetocrystalline anisotropy energy, and strain-generated magnetoelastic energy. This study is helpful for understanding the electric-field control of magnetism in multiferroic heterostructures as well as its relevant applications.

Temperature‐ and E‐field‐dependent domain configuration and electrical properties in (K, Na, Li)(Nb, Ta, Sb)O3 single crystal

AbstractE‐field‐ and temperature‐dependent domain evolution of lead‐free tetragonal (K, Na, Li)(Nb, Sb, Ta)O3 (KNLNTS) single crystals as well as its corresponding electrical properties have been investigated. When E field is applied along [011]C direction, (2T) engineered domain structure is formed. Spontaneous polarizations switch under a critical electric field (around 4‐5 kV/cm), resulting in significant changes in domain structure and great improvement in piezoelectric properties. Furthermore, it is found that piezoelectric constant d31 and electromechanical coupling factor k31 of [011]C poled KNLNTS single crystal decrease with temperature. The extrinsic and intrinsic piezoelectric responses are discussed from the viewpoint of domain structure and lattice distortion, respectively. Our results show that the nanodomain structure relaxes and the lattice distortion declines with temperature, resulting in reduction of extrinsic and intrinsic piezoelectric responses, respectively. Therefore, the piezoelectric instability is ascribed to the decrease of both extrinsic and intrinsic contributions. This work provides a better understanding of domain engineering technique, and the useful information on the improvement of both piezoelectricity and temperature stability of the lead‐free piezoelectric materials.

Switching Characteristics and High-Temperature Dielectric Relaxation Behaviours of Pb(Zn1/3Nb2/3)0.91Ti0.09O₃ Single Crystal.

This work evaluated the resistance switching characteristics in the (100)-oriented Pb(Zn1/3Nb2/3)0.91Ti0.09O3 (PZNT) single crystal. The current hysteresis can be closely related to the ferroelectric polarization and we provided a possible explanation using a model about oxygen vacancies to analyze the mechanism of switching. The obvious frequency dispersion of the relative permittivity signified the relaxer-type behavior of the sample. The value of the relaxation parameter γ = 1.48 was estimated from the linear fit of the modified Curie-Weiss law, indicating the relaxer nature. High-temperature dielectric relaxation behaviors were revealed in the temperature region of 400–650 °C. In addition, under the measuring frequency of 10 kHz, εr was tunable by changing the electric field and the largest tunability of εr reached 14.78%. At room temperature, the high pyroelectric coefficient and detectivity figure of merit were reported.

Magnetic Properties of La3Ga5.5Ta0.5O14 Single Crystals Doped with Sm3+ and Er3+ Ions

Magnetic Properties of La₃Ga_5.5Ta_0.5O₁₄ Single Crystals Doped with Sm³⁺ and Er³⁺ Ions

Field induced phase transitions and energy harvesting performance of (Pb,La)(Zr,Sn,Ti)O3 single crystal

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with composition close to the morphotropic phase boundary had been grown by the flux method. The antiferroelectric-ferroelectric phase switching electric field was 0.8 kV/mm. Temperature-dependent dielectric and polarization versus electric field hysteresis loops revealed that the electric field induced ferroelectric phase could transform back into the antiferroelectric phase at depolarization temperature (145 °C). An enhanced pyroelectric coefficient value of 1.46 μC/cm2/K was obtained at 145 °C, which is several times larger than that of conventional pyroelectric materials. Furthermore, multiple peak pyroelectric responses and an enhanced harvested energy density value of 0.4 J/cm3 were achieved in the PLZST crystal. The enhanced harvested energy density and multiple peak pyroelectric responses make the PLZST crystal a promising candidate for high sensitive temperature sensors and energy conversion technologies.

Phase transformations, anisotropic pyroelectric energy harvesting and electrocaloric properties of (Pb,La)(Zr,Sn,Ti)O3 single crystals.

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with their chemical composition located at the tetragonal antiferroelectric region are grown via the flux method in a PbO-PbF2-B2O3 mixture. Segregation of the Ti4+ component in the as-grown crystals is observed due to the strong affinity between the oxygen anion and Ti4+ ions. The critical electric field of the antiferroelectric to ferroelectric phase transition is determined to be about 0.5 kV mm-1. The electric field induced ferroelectric phase transforms back into the antiferroelectric phase at a depolarization temperature of 125 °C. Anisotropy of the harvested energy density and electrocaloric behaviors are achieved for the [100], [110] and [111]-oriented PLZST crystals. Based on the thermodynamic theory approach, all the abovementioned behaviors originate from the anisotropic total entropy change. Enhanced electrocaloric strength (0.3 K mm kV-1) and the harvested energy density of 0.62 J cm-3 are obtained in the [111]-oriented PLZST crystals. Our results demonstrate the competence of PLZST single crystals for cooling devices and pyroelectric energy harvesting and provide new opportunities to improve energy harvesting density and electrocaloric properties via the anisotropic structural layout, which make the PLZST crystals attractive for solid state cooling devices and energy conversion technologies.

Combining two redox active rare earth elements for oxygen storage - electrical properties and defect chemistry of ceria-praseodymia single crystals.

Solid solutions of ceria and praseodymia are highly relevant for electrochemical applications as the incorporation of praseodymium into the ceria lattice shifts the range of mixed ionic electronic conductivity to higher oxygen partial pressures. To better understand the influence of praseodymium substitution on the transport processes and oxygen storage capacity in ceria, single crystals of ceria substituted with 14 mol% praseodymium have been investigated, obtaining the bulk properties without the influence of grain boundaries. Beside the characterization of structural changes caused by the substitution using XRD and Raman spectroscopy, the electrochemical transport properties of ceria-praseodymia single crystals are reported. Measurements of the total electrical conductivity, the ionic transference number and the non-stoichiometry of Ce0.85Pr0.14Zr0.01O2-δ were performed in an oxygen partial pressure range of -25 < lg[p(O2)/bar] < 0 at 700 °C. With praseodymium being redox active itself, higher values of oxygen deficiency and electrical conductivity than in pure ceria have been observed in the high oxygen partial pressure region, while no significant structural changes occur due to the similar ionic radii of both cations. From measurements of the impedance at different temperatures, the migration enthalpy for the electronic charge carriers has been determined. By analysing the non-stoichiometry at 700 °C using a defect chemical model it was also possible to determine the equilibrium constants of Pr and Ce reduction in Ce0.85Pr0.14Zr0.01O2-δ single crystals.

Investigations on magnetic properties of La3Ga5.5Ta0.5O14 single crystals doped with Er3+ ions

La3Ga5.5Ta0.5O14 (LGT) single crystals doped with 3.8 at. % of Er3+ ions have been investigated by performing Electron Paramagnetic Resonance (EPR) and magnetic susceptibility measurements. The results of EPR measurements show a large anisotropy of spin Hamiltonian parameters belonging to isolated erbium centers. In addition to the isolated erbium centers a small number of pairs of erbium ions was also observed. Based on the obtained spin Hamiltonian parameters we have determined the symmetry of isolated and paired erbium ions as being at least C4. From magnetization measurements it does not result strong coupling between Er3+ ions and the lattice of LGT crystals.

Raman spectra of (K, Na)(Nb, Ta)O3 single crystal

Abstract The Raman scattering spectra for lead-free piezoelectric single crystal (K,Na)(Nb,Ta)O3 (KNNT) were intensively investigated to explore its crystallographic structure. For the [011]C oriented sample, 12 Raman peaks were identified from the room temperature Raman spectrum. The υ3, υ4 and υ6 modes which should be Raman silent in normal perovskites were observed due to the low symmetry (Pm) of KNNT single crystal. The temperature dependent Raman spectra indicated that the orthorhombic-tetragonal phase transition happened at about 68 °C, and the Curie temperature (TC) is about 225 °C. The merging of 2 υ5 modes at TC was ascribed to the vanishing of polarization. The backscattering polarized Raman spectra of KNNT single crystals with different orientations were analyzed. The Raman modes were identified using polarized selection rules based on group theory.

Orientation-dependent electromechanical properties of Mn-doped (Li,Na,K)(Nb,Ta)O3 single crystals

Orientation and temperature dependence of dielectric and electromechanical properties of Mn-doped (Li,Na,K)(Nb,Ta)O3 single crystals were investigated. Samples exhibited very low dielectric losses, with tanδ between 0.03 and 0.05 over a broad temperature range between room temperature and 480 °C. Influences of the crystallographic structure and external electric field on polarization and strain parameters are discussed. The orientation-dependent electrical properties were ascribed to the anisotropic polarization rotation in the crystals. Higher maximum polarization, coercive field, and negative strain were achieved when the electric field was oriented along one of the spontaneous polarization directions. The highest maximum unipolar strain of 0.42% (at 3 kV/mm) and the normalized strain d33* of 1391 pm/V were obtained in the [001]PC-oriented sample at 100 °C, which was much higher than the values obtained for the [110]PC-oriented sample. Further insight of the phase transition behavior is given by comparing the temperature-dependence of the small- and large-signal dielectric and piezoelectric properties. The observed changes are rationalized by the different increase rates of the dielectric permittivity and piezoelectric coefficients with temperature.

Structure and dielectric characteristics of PbFe0.5Nb0.5O3 single crystals grown under different conditions

The structure and dielectric and magnetic characteristics of plumbum ferroniobate crystals grown from a solution–melt containing potassium fluoride have been investigated. The obtained crystals have a cubic shape, 4-mm edges, and a rhombohedral structure at room temperature. Iron ions in the samples have the valence state of Fe3+. A change in the Mossbauer spectra with a change in temperature has been registered; this is indicative of strong diffusion of the magnetic phase transition in the range from–130 to–230°C, which is enhanced due to incorporation of fluorine atoms into the structure of the basic compound accompanying the synthesis process and clusterization of this structure. The latter phenomena also lead to a decrease in the temperature of transition from the ferro- to paraelectric phase.

Full tensor properties of [111]C poled (Na, K)(Nb,Ta)O3 lead-free single crystal

Complete sets of elastic, piezoelectric and dielectric constants of [111]C poled (Na,K)(Nb, Ta)O3 single crystal have been measured. The results show that the crystal with “3O” domain structure exhibits high shear but low longitudinal piezoelectric properties (d15=140 pC/N, k15=0.569, d33=64 pC/N and k33=0.450), which is similar to the “1O” single domain state, but different from the “4O” multi-domain state. The orientation-dependent longitudinal properties, e.g., d33*, ε33*, s33* and k33* in the (01¯1)C plane have been calculated. The maximum piezoelectricity exists at the position of 38° away from [011]C, which is close to the [111]C direction. By comparing the measured and calculated parameters, it can be concluded that the piezoelectricity is dominated by the intrinsic contribution while the dielectricity is controlled by the extrinsic contributions.

Magnetic properties and spin reorientation of perovskite SmFe 0.5 Mn 0.5 O 3 single crystal

Abstract The crystal structure and magnetic properties of the rare-earth perovskite SmFe0.5Mn0.5O3 single crystal were studied. The single crystal was successfully synthesized by optical-floating-zone method. M-T and M-H curves were measured to study the magnetic state in the single crystal. Strong magnetic anisotropy was observed in temperature dependent magnetization measurements along three crystallographic axes a, b and c. The first magnetic phase transition at TN=286 K is paramagnetic to antiferromagnetic transition. The M-T curve then undergoes a second intriguing transition from 254 K to 244 K and this transition is spin orientation from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) due to anisotropic Mn3+ ions and complex interaction in our sample. Magnetic transition of rare earth oxides was tuned by Mn3+ doping, which has potential for future application.

Domain structures and correlated out-of-plane and in-plane polarization reorientations in Pb(Zr0.96Ti0.04)O3 single crystal via piezoresponse force microscopy

Pb(Zr1-xTix)O3 single crystal with a low titanium content (x = 4%) was studied by the piezoresponse force microscopy (PFM) and X-ray diffraction (XRD). The XRD studies showed that the crystal faces are orthogonal to the principal cubic axes and confirmed the existence of an intermediate phase between the high-temperature paraelectric (PE) phase and the low-temperature antiferroelectric (AFE) one. A significant temperature hysteresis of phase transitions was observed by the XRD: On heating, the AFE state transforms into the intermediate one at about 373 K and the PE phase appears at 508 K, whereas on cooling the intermediate phase forms at 503 K and persists down to at least 313 K. The PFM investigation was focused on the intermediate phase and involved measurements of both out-of-plane and in-plane electromechanical responses of the (001)-oriented crystal face. The PFM images revealed the presence of polarization patterns switchable by an applied electric field, which confirms the ferroelectric character of the intermediate phase. Importantly, two types of regular domain structures were found, which differ by the spatial orientation of domain walls. The reconstruction of polarization configurations in the observed domain structures showed that one of them is a purely ferroelectric 180° structure with domain walls orthogonal to the crystal surface and parallel to one of the ⟨111⟩ pseudocubic directions. Another one is a ferroelectric-ferroelastic domain structure with the 71° walls parallel to the {101} or {011} crystallographic planes. Remarkably, this domain structure shows correlated out-of-plane and in-plane polarization reorientations after the poling with the aid of the microscope tip.