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13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Simultaneous holographic and photocurrent studies of the photorefractive effect in LiTaO3 and LiNbO3

In reduced LiNbO3:Mn both the photorefractive sensitivity and the simultaneously measured photocurrent result from drift with a polarization-dependent effective 'internal field' of about 6 kV/cm. In reduced undoped LiTaO3 the observed difference in applied fields of the minimum photorefractive sensitivity and zero photocurrent imply charge transport is by a mechanism that cannot be completely described by diffusion and drift in an electric field. The direct measurement of the harmonic content of phase gratings written in several LiNbO3 and LiTaO3 crystals shows termination of charge-transport results from the space-charge field of the hologram.

Spinhirne, J. M.↗
DOE OSTI2020

Materials Data on LiTaO3 by Materials Project

LiTaO3 is Ilmenite-like structured and crystallizes in the trigonal R3c space group. The structure is three-dimensional. Li1+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. There are three shorter (2.08 Å) and three longer (2.31 Å) Li–O bond lengths. Ta5+ is bonded to six equivalent O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 38°. There are three shorter (1.93 Å) and three longer (2.09 Å) Ta–O bond lengths. O2- is bonded in a distorted see-saw-like geometry to two equivalent Li1+ and two equivalent Ta5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTaO3 by Materials Project

LiTaO3 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are four shorter (2.43 Å) and four longer (2.72 Å) Li–O bond lengths. In the second Li1+ site, Li1+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.43 Å) and four longer (2.72 Å) Li–O bond lengths. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 0–30°. There is two shorter (1.97 Å) and four longer (1.99 Å) Ta–O bond length. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 0–30°. There is two shorter (1.97 Å) and four longer (1.99 Å) Ta–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four Li1+ and two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded to two equivalent Li1+ and two Ta5+ atoms to form a mixture of distorted edge and corner-sharing OLi2Ta2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTaO3 by Materials Project

LiTaO3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with six equivalent LiO6 octahedra, corners with four equivalent TaO4 tetrahedra, and edges with two equivalent TaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 47–48°. There are a spread of Li–O bond distances ranging from 2.07–2.34 Å. Ta5+ is bonded to four O2- atoms to form TaO4 tetrahedra that share corners with four equivalent LiO6 octahedra, corners with two equivalent TaO4 tetrahedra, and edges with two equivalent LiO6 octahedra. The corner-sharing octahedra tilt angles range from 43–78°. There are a spread of Ta–O bond distances ranging from 1.81–1.96 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted see-saw-like geometry to two equivalent Li1+ and two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Li1+ and one Ta5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTaO3 by Materials Project

LiTaO3 is Ilmenite-like structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Li1+ is bonded to six O2- atoms to form distorted LiO6 octahedra that share corners with six equivalent LiO6 octahedra, corners with four equivalent TaO6 pentagonal pyramids, and edges with four equivalent TaO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 54–59°. There are a spread of Li–O bond distances ranging from 1.97–2.48 Å. Ta5+ is bonded to six O2- atoms to form distorted TaO6 pentagonal pyramids that share corners with four equivalent LiO6 octahedra, corners with two equivalent TaO6 pentagonal pyramids, edges with four equivalent LiO6 octahedra, and edges with two equivalent TaO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 52–77°. There are a spread of Ta–O bond distances ranging from 1.92–2.09 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Li1+ and two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded to two equivalent Li1+ and two equivalent Ta5+ atoms to form a mixture of distorted corner and edge-sharing OLi2Ta2 trigonal pyramids.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Sensitivity and fatigue of LiTaO3 for holographic recording

The sensitivity of crystals of LiTaO3 to hologram formation was observed to vary with impurity concentration from a value comparable to the most sensitive doped LiNbO3 for an impure crystal to a value more than five orders of magnitude smaller for a purer crystal. Fatigue effects were observed upon write-erase cycling. These effects were dependent upon writing and erasure polarization and power and could be virtually eliminated by proper choice of optical parameters.

Spinhirne, J. M.↗
NASA NTRS1974

Sensitivity and fatigue of LiTaO3 for holographic recording

The sensitivity of LiTaO3 crystals to hologram formation has been observed to vary with impurity concentration. For a writing wavelength of 488.0 nm and power density of 1.1 W/sq cm, the sensitivity varied from a value comparable to the most sensitive doped LiNbO3 for an impure crystal to a value more than 5 orders of magnitude smaller for a purer crystal. Fatigue effects were observed upon write-erase cycling. These effects were dependent upon writing and erasure polarization and power density and could be minimized by proper choice of optical parameters.

Spinhirne, J. M.↗
DOE OSTI2020

Latent Tracks in Ion-Irradiated LiTaO 3 Crystals: Damage Morphology Characterization and Thermal Spike Analysis

Systematic research on the response of crystal materials to the deposition of irradiation energy to electrons and atomic nuclei has attracted considerable attention since it is fundamental to understanding the behavior of various materials in natural and manmade radiation environments. This work examines and compares track formation in LiTaO3 induced by separate and combined effects of electronic excitation and nuclear collision. Under 0.71–6.17 MeV/u ion irradiation with electronic energy loss ranging from 6.0 to 13.8 keV/nm, the track damage morphologies evolve from discontinuous to continuous cylindrical zone. Based on the irradiation energy deposited via electronic energy loss, the subsequently induced energy exchange and temperature evolution processes in electron and lattice subsystems are calculated through the inelastic thermal spike model, demonstrating the formation of track damage and relevant thresholds of lattice energy and temperature. Combined with a disorder accumulation model, the damage accumulation in LiTaO3 produced by nuclear energy loss is also experimentally determined. The damage characterizations and inelastic thermal spike calculations further demonstrate that compared to damage-free LiTaO3, nuclear-collision-damaged LiTaO3 presents a more intense thermal spike response to electronic energy loss owing to the decrease in thermal conductivity and increase in electron–phonon coupling, which further enhance track damage.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Development of improved lithium tantalate pyroelectric detectors

A program was undertaken to increase the detectivity of LiTaO3 pyroelectric detectors to meet a performance requirement of D star (500 K, 15 Hz)=4x10 to the 9th power cm Hz1/2W-1. Emphasis was placed on reduction of the thermal conductance of the detector element to its surroundings, thinning the detector wafer to a thickness less than 3 micrometers, and increasing the absorptivity of the standard metallic film coatings. During the program, thermal conductance was reduced 41 percent through the use of reticulated (slotted) structures. Self-supported detector wafers less than 2 micrometers thick were fabricated. Multiple layer coatings, including an AR coating, with 16 percent more absorptance, were designed and fabricated. Later refinements in the multilayer design program have absorptivities of 75-80 percent, but detectors with these coatings had to be more than 2 micrometers thick because of a mismatch in the thermal expansion coefficients with LiTaO3.

Byer, N. E.↗
DOE OSTI2026

Nanoscale Compositional and Strain Gradients Enable High‐Speed and Amplitude‐Resolved Pyroelectric Sensing

The frequency response of pyroelectric sensors is fundamentally governed by thermal time constant (τth, determined by thermal mass and thermal conductance) and electrical impedance arising from film capacitance and readout circuit. Conventional bulk LiTaO3 detectors are optimized for high responsivity at low modulation frequencies (0.1-10 Hz), possessing a large τth that thermally averages rapid temperature oscillations at elevated modulation frequencies, limiting fidelity in resolving dynamic varying thermal signals. Here, compositional and strain gradients are introduced into 100-nm-thick relaxor-ferroelectric films reducing τth to ≈2 µs and producing built-in potentials (≈1.45 V or 145 kV cm-1) that enhance the pyroelectric coefficient and suppress the dielectric constant. This enables complementary dual-mode operation by enhancing current-mode electrical responsivity and improving the voltage-mode figure of merit - advantageous for superior temperature resolution (ΔTmin ≈ 30 µK). The responsivity peak shifts to near 1 kHz (>2500-times higher than conventional bulk sensors), with measurable responsivity extending to a carrier frequency of 100 kHz and amplitude-resolved detection at modulation frequencies up to 15 kHz. These results establish nanoscale internal-field engineering can reshape electro-thermal trade-off in pyroelectric thin films toward zero-bias, high-thermal-sensitivity, and amplitude-resolved thermal sensing across a wide frequency bandwidth.

Lin, Ching‐Che↗
DOE OSTI2021

Ion irradiation induced strain and structural changes in LiTaO 3 perovskite

LiTaO 3 crystals irradiated with 3 MeV and 1.162 GeV Au ions were studied by single crystal x-ray diffraction and Raman scattering measurements. The maximum lattice strains after 3 MeV Au ion irradiation to a fluence of 1.2 × 10 13 cm -2 were 1.2% and 0.6% along the c- and a-/b-axes, respectively. Two effects were observed in 1.162 GeV Au ion irradiated samples: (i) the (0006) and (1120) Bragg peaks were split into doublets, which suggested a subtle structural change due to slight modification of chemical composition; and (ii) the pre-damaged 1.2% lattice strain along the c-axis was relaxed to 0.9% after subsequent irradiation with 1.162 GeV Au ions, while relaxation along the a- or b-axis was not obvious. A distinct change in the Raman spectrum of the <0001> oriented LiTaO 3 crystals was observed after 1.162 GeV Au ion irradiation, but no obvious change was observed in the <1120> oriented samples or in 3 MeV Au ion irradiated samples. Strain and structural changes in crystalline LiTaO3, with or without pre-existing defects, upon ion irradiation are delineated in its responding to inelastic ionization and elastic nuclear collisions.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Alkali oxide-tantalum oxide and alkali oxide-niobium oxide ionic conductors

A search was made for new cationic conducting phases in alkali-tantalate and niobate systems. The phase equilibrium diagrams were constructed for the six binary systems Nb2O5-LiNbO3, Nb2O5-NaNbO3, Nb2O5-KNbO3, Ta2O5-NaTaO3, Ta2O5-LiTaO3, and Ta2O5-KTaO3. Various other binary and ternary systems were also examined. Pellets of nineteen phases were evaluated (by the sponsoring agency) by dielectric loss measurements. Attempts were made to grow large crystals of eight different phases. The system Ta2O5-KTaO3 contains at least three phases which showed peaks in dielectric loss vs. temperature. All three contain structures related to the tungsten bronzes with alkali ions in non-stoichiometric crystallographic positions.

Roth, R. S.↗
NASA NTRS1984

Pyroelectric materials as electronic pulse detectors of ultraheavy nuclei

The design and testing of ultraheavy-nucleus pulse detectors based on pyroelectric materials are reported, extending the preliminary findings of Tuzzolino (1983) and Simpson and Tuzzolino (1983). Uranium-ion beams of about 240 MeV/u are detected by a 39.5-micron-thick Si detector, degraded to about 175 MeV/u by Al absorbers, and then strike 700-micron-thick polyvinylidene fluoride or 1000-micron-thick LiTaO3 pyroelectric samples. Both detector systems are connected to a coincidence circuit via charge-sensitive preamplifiers, shaping amplifiers with 30-microsec effective time constants, and electronic discriminators. Sample spectra are shown, and the pulse heights measured are found to agree with theoretical calculations to within a factor of about 2. The response of the pyroelectric materials is found to be unaffected by exposure to about 10 Mrad of 2-7-MeV/u heavy ion radiation. With further study and improvement of the detection sensitivity, devices of this type could be applied to large-area space measurements of low ultraheavy-ion fluxes.

Simpson, J. A.↗