Barium Sodium Niobate Research Articles

High-frequency resonance in acoustic superlattice of barium sodium niobate crystals

By using growth striation technique, an acoustic superlattice of barium sodium niobate crystals, the single crystals with the periodic laminar ferroelectric domain structures, has been prepared. High-frequency resonance in the range of 200–400 MHz in such materials has been realized experimentally. The experimental results indicate that the application of acoustic devices with low acoustic loss operating at high frequencies is expected.

On the Theory of Soliton Lattice Melting in Three‐Dimensional Incommensurate Cystals

AbstractThe transition into the normal phase, associated with the melting of the soliton lattice in the incommensurate phase of a three‐dimensional crystal, is theoretically studied. It is shown, that in barium−sodium niobate (BSN) crystals this transition can take place in two steps.

Phase-Matching of Optically Second-Harmonic Generation in the Single Crystals of Gd- and La-Added Barium Sodium Niobate

Optically microscopic observation, measurements of the phase-matching temperature of second-harmonic generation (SHG) and evaluation of the SHG conversion efficiency were carried out for three kinds of single crystals: barium sodium niobate (BNN), La-added BNN [BN(La)N] and Gd-added BNN [BN(Gd)N]. The best crystalline-quality crystal was [BN(Gd)N] and the crystal showing the highest SHG conversion efficiency was also [BN(Gd)N]. The phase-matching temperatures were about 120°C and 160°C. Some discussion was given on the SHG phase-matching.

Raman spectroscopy of incommensurate Ba2NaNb5O15.

We have performed Raman studies of the E-symmetry phonon modes in barium sodium niobate in the tetragonal ferroelectric phase above 582 K and measured carefully their splitting into pairs of ${\mathit{B}}_{1}$ and ${\mathit{B}}_{2}$ symmetry in the incommensurate (IC) phase between 543 and 582 K. For both heating and cooling cycles the data satisfy mean-field predictions with ${\mathit{B}}_{1}$-${\mathit{B}}_{2}$ frequency splitting proportional to the order parameter. The data show that the incommensurate-incommensurate transition at 565 K (heating) does not alter the orthorhombic symmetry; that is, it is not a true 1q-2q transition, and tetragonal symmetry does not set in until the incommensurate-normal transition at 582 K. This is compatible with very recent electron microscopy data (Verweft, Van Tendeloo, and Van Landuyt), which show that the incommmensurate-incommensurate transition near 565 K produces only short-range order in a direction perpendicular to the long-range 1q modulation, and with x-ray studies of this transition (Kiat, Toledano, and Schneck). An analogous situation is observed just below the incommensurate-commensurate transition at 105 K: Here the ${\mathit{C}}_{11}$ and ${\mathit{C}}_{22}$ elastic coefficients have minima at 105 K, signaling a phase transition, but they do not become equal (${\mathit{C}}_{11}$=${\mathit{C}}_{22}$) until approximately 90 K, indicating that there is an incommensurate-incommensurate transition from orthorhombic to tetragonal near 90 K. The 90-K IC-IC transition seems quite analogous to the 565-K IC-IC transition, but electron microscopy shows that these phases are not reentrant.

Influence of defects on the incommensurate modulation in irradiated Ba2NaNb5O15.

Defect-induced properties of barium sodium niobate (Ba{sub 2}NaNb{sub 5}O{sub 15}) have been studied as a function of electron irradiation dose. Birefringence measurements at low doses indicate that the lock-in transition temperature, originally at about 280 {degree}C, decreases linearly with increasing dose. Complementary irradiations {ital in} {ital situ} in a high-voltage electron microscope show that the incommensurate phase can be stabilized down to room temperature. Simultaneously the satellite diffraction spots broaden and the lock-in transition becomes diffuse. The modification of the hysteresis of the birefringence, observed already at the lowest doses, indicates a progressive extension of the stability range of the 2{ital q} modulated phase to lower temperatures as the defect concentration increases. A similar conclusion can be drawn from the satellite reflection dark-field electron micrographs that show, once the incommensurate phase is stabilized at room temperature, the doubly modulated texture characteristic of the 2{ital q} modulated phase. Low doses of irradiation do not change qualitatively the configuration of the residual discommensurations in the lock-in phase nor the temperature dependence of the incommensurability. Accordingly, already in the as-grown samples the defects dominate the pinning of the incommensurate modulation and the intrinsic properties of this incommensurate system are not clearly observable.

Thermostimulated erasure of photorefraction (TSEP) and the study of trap energy spectrum in photorefractive ferroelectrics

Abstract A novel technique of trap center energy determination is proposed and tested in LiNbO3 and Ba2NaNb5O15 crystals. More than ten different levels with activation energies ranging from 0.25 to 0.69 eV were found for barium sodium niobate, but only two levels, 0.28 and 0.38eV, for lithium niobate crystals.

Evaluation of critical exponents from raman intensities

Abstract Theory and experiment are compared for Raman intensities near continuous structural phase transitions. Situations in which the order parameter couples linearly to light or quadratically are considered. Both cases are easily analyzed for the soft modes in ferroelastic LnP5O14 (Ln = La, Pr, Nd, Tb). The trace polarizability tensor yields β = 0.49 ± 0.02; off-diagonal terms give γ’ = 1.16 ± 0.15 and γ = 1.07 ± 0.10. Mean field results are also obtained for barium sodium niobate near T (incommensurate) = 582 K and for tris-sarcosine calcium chloride near T c = 128 K.

Sol-Gel Derived Barium Sodium Niobate and Bismuth Titanate Films

AbstractSol-gel derived barium sodium niobate and bismuth titanate films were successfully prepared from precursor solutions of chelated Ba[Nb(OEt)6]2 and NaNb(OEt)6 and from bismuth 2-ethyl hexanoate and Ti(OEt)4 respectively. Single phase Ba2NaNb5O15 was formed at 750C on platinized Si and at 850C on fused SiO2. Monoclinic (pseudo-orthorhombic) Bi4Ti3O12 was formed at temperatures as low as 500C. Both film compositions showed significant second harmonic generation. The dielectric constant of the bismuth titanate film was comparable to that of sputtered films.

Low temperature elastic and dielectric properties of incommensurate barium sodium niobate

We have performed dielectric and Brillouin spectroscopic measurements on incommensurate (IC) Ba2NaNb5O15 from ca. 15 K to room temperature and have related our measurements to earlier studies of birefringence and x-ray and neutron crystallography, with special emphasis upon the structural phase transitions near 105 K and 40 K. The 105 K transition is from Bbm2 to a modulated structure, which appears to be a reentrant phase also found at atmospheric pressure from 565 K to 582 K. Such a reentrant IC/C/IC sequence is predicted in the phenomenological theory of Ishibashi. The lock-in phase below 40 K is tetragonal and probably of space group P4nc (structural refinements of preliminary neutron scattering data are in progress).

Effect of gadolinium content on the thermal volume change of Ba4Na2Nb10O30 ? Ba3NaGdNb10O30 solid solutions at ferroelectric phase transition temperature

For sintered samples of Ba3+x Na1+xGd1−xNb10O30 (1 ⩾x ⩾ 0), the effect of the addition of gadolinium to barium sodium niobate (BNN,x = 1, tungsten bronze type) was examined by differential scanning calorimetry (DSC) and X-ray powder diffractometry. The volume change (i.e. especially the change ofc-axis length) at the ferroelectric phase transition temperature (Tc< 590 dg C) decreased with the increasing gadolinium content. This result suggests that the addition of gadolinium or other lanthanide elements to BNN is possibly effective to obtain an uncracked single crystal with the Czochralski technique. The DSC indicator method is useful to determine the relative magnitude of volume change atTc for the same type of sample series, a method which is much easier than the dilatometer method. The relation between the DSC peak area and the volume change of unit cell atTc is discussed from the thermodynamic viewpoint.

GROWTH OF UNCRACKED BARIUM-SODIUM NIOBATE CRYSTALS

It is known that cracking occurs in Barium-Sodium Niobate, Ba 4 Na 2 Nb 10O30 (BNN), during Czochralski (cz) growth. This is due mainly to lattice distortions associated with the ferroelectric phase transition. We have studied the cz crystal growth condition for BNN without cracking, and found that high quality single crystals of BNN without cracking can be grown by using Gd-doped starting melt, i.e., Ba 4 Na 2 Nb 10O30-Ba3NaGdNb10O30 solid solution. In order to confirm the effect of Gd doping on the crystalline quality, Gd concentrations were measured by ICP for both the cz single crystal sample and the starting powder material. Gadlinium concentration in the as-grown crystal was about 0.195 mol %, nearly the same as that (2.0 mol %) in the starting material. Dielectric constant along c-axis, ε33, was measured at temperatures from 300 K to 870 K. The experimental result revealed that ε33 of the single crystal is about two times larger than that of BNN single crystal without Gd impurity in the temperature range from 300 K to 650 K.

Electron microscopy study of incommensurate modulation in barium sodium niobate

Abstract Electron diffraction and high resolution electron microscopy (HREM) have been employed to investigate the incommensurate modulation in barium sodium niobate (BSN). Especially, we have characterized the texture of the phase front at the lock-in transition through the proper heat treatment of speciments. We have observed that the stable phase near Tc is the singly-modulated orthorhombic phase. The topological features of the discommensurations and the characteristics of the corresponding electron diffration pattern have been presented.

Thermally induced optical damage to barium–sodium niobate crystals

Thermally induced optical damage (TIOD) was observed in undoped barium–sodium niobate (BSN) crystals as a result of changes in their temperature. This damage was deduced from the behavior of YAG:Nd3+ laser radiation when a BSN crystal was inserted in the resonator and also using a helium–neon laser probe beam. The experimental results were satisfactorily explained by the familiar pyroelectric model of TIOD and, in the crystals studied, an inhomogeneity of the conductivity rather than an inhomogeneity of the pyroelectric constant played the main role.

TEM study of the 1q to 2q transition within the incommensurate phase of barium sodium niobate

Abstract A complementary study of the phase transition in barium sodium niobate by electron microscopy and electron diffraction was performed. Nucleation and multiplication of microscopic domains were examined on heating. These processes correspond to the appearance of the 2q-incommensurate phase. Experimental results show that the large thermal hysteresis, the complex memory effect, and the slow relaxation are related to the coexistence of the 1q- and 2q-phases.

Coexistence of 2Q and 1Q states and memory effect in B.S.N

Abstract It is shown that the wide thermal hysteresis of the misfit parameter in incommensurate barium sodium niobate is related to the coexistence of the 1q and 2q incommenurate phases. The complex nature of the memory effect is studied and discussed in connection with the occurrence of this mixing of phases.

Studies of incommensurate barium sodium niobate

Abstract New studies are reported on three different phases of barium sodium niobate: In the lowest-temperature “lock-in” phase from 0 – 40K, three different space group symmetries have been predicted theoretically (J. Schneck, Thesis, Univ. Paris, 1982) –P42bc, P4nc, and Bb. The present neutron study shows that P4nc is correct. In the incommensurate phase from 543K to 582K we find a dynamic central mode with width ca. 20 GHz that peaks in Raman intensity at 565K, in the middle of the IC phase within IK of the lq to 2q (orthorhombic to tetragonal) transformation inferred from the electron microscopy data (Feng Duan and Pan Xiaoqing, 1986). The q2 dependence of central mode linewidth yields a value of zero for the gap energy (upper limit of 8 GHz), and the novel technique of measuring the ratio of intensities for forward and back-scattering yields a value of (12+3)% for the ratio of incommensurate modulation to the lattice constant (i.e., ca 0.2A distortion). This dynamic central mode may be related to the anti-phase boundary roughening transition predicted by Rice et al. Finally, the highest temperature transition, at Curie temperature 855K, is studied by boch dynamic central mode light scattering and a newly discovered thermal lens effect; these two techniques yield quite different diffusivities, indicating that more than one diffusion process is important near TC.

Dynamic evolution of discommensurations during the commensurate-incommensurate transition in barium sodium niobate

The temperature evolution of discommensuration (DC) during the heating run through the commensurate-incommensurate (C-I) transition in barium sodium niobate is investigated by means of transmission electron microscopy. It is found that the interaction of DC is attractive over considerable distances, and that frozen-in DC become meandering and collide with each other in the process of reducing the DC density under the influence of thermal fluctuations at a temperature below the lock-in transition. A transient metastable state (or chaotic state) is observed with successive nucleation of DC in the early stages of transition, and later a wavy DC array is formed. DC loops with high density of DC are formed at a temperature above the C-I transition. A qualitative theoretical explanation of the observed characteristics on the evolution of DC is presented based on a Landau theory.

Structural and electrical properties of Dy-doped barium sodium niobate ceramics

Abstract It is proposed to discuss the experimental results concerning the influence of the Dy3+ amount of Barium Sodium Niobate (BNN) ceramics on their structural and electrical properties in this paper. X-ray diffraction, SEM, electrical (dielectric and resistivity), and piezoelectric measurements were carried out for ceramics of composition Ba4-2xNa2 + xDyx 3+Nb10O30 with x = 0.3, 0.5 and 0.7 processed by the usual ceramic method. X-ray diffraction studies showed a single phase in all the compositions with a tetragonal tungsten bronze (TB) symmetry. SEM micrographs reveal an inhibition of grain growth with Dy and is in the range 1 ∼ 3 μm. The room temperature dielectric constant, broadening of the dielectric constant versus temperature curves are observed to increase and the ferroelectric curie temperature (Tc ) decreases with the Dy concentration. It is interesting to note that a PTC effect has been observed in all the compositions and the region of the section of PTC shifted to higher temperatures wi...

X-ray structural determination of the quasi-commensurate phase of barium sodium niobate

In order to provide an accurate basis for the interpretation of the physical properties of this complex incommensurate system, the structure of the room temperature quasi-commensurate phase of barium sodium niobate is determined by taking into account, for the first time, the satellite reflections present in the diffraction spectrum of this material. The quasi-commensurate phase considered is assimilated to a strictly commensurate phase, the satellite reflections being considered as superlattice reflections and referred to a crystalline supercell with a=35.187 AA, b=17.620 AA and c=7.987 AA. This approximation gives an excellent agreement index R=0.031 for the fit to the intensities of the 2432 basic reflections and the 1691 satellite reflections collected at 294 K ( lambda Mo K alpha =0.71069 AA, mu 1=111.47 cm-1, space group Bbm2). The structural results show that the commensurate modulation consists of a tilting and a shearing of all the NbO6 octahedra in the structure in contrast to previous inferences which had only suggested the occurrence of a shear. The framework of the structure may be described on the basis of the existence of two different Nb5O24 units of five corner-sharing octahedra each. The structure obtained by spatially averaging the modulation is consistent with previous structural studies of the basic reflections of this material. Physical characteristics pertaining to the polar character, or the domain structure, are also deduced.

Domain structures induced by defects in Ba2NaNb5O15and LiNbO3

Abstract Systematic observations of ferroelectric and ferroelastic domains induced by defects, such as dislocations, inclusions and twins, are reported for as-grown barium sodium niobate and lithium niobate crystals. The main characteristics of defect-induced domains in these crystals are described. It is found that shapes of ferroelectric domains induced by dislocations depend upon directions of dislocation lines and domain structures of matrix in both crystals, and are related with the Burgers vectors in LiNbO3 but are independent of them in Ba2NaNb5O15.