Yao Xi

The growth and properties of a new alanine and phosphate substituted triglycine sulphate (atgsp) crystal

A modified alanine doped triglycine sulphate (ATGS) crystal has been grown with partial substitution of H2SO4 with H3PO4. Growth of the ATGSP crystal from a unipolar ATGS seed in the temperature range 30-40°C gives a unipolar bulk crystal with lower permittivity (er ∼ 30) and higher pyroelectric coefficient (6.5·10-4 c/k.m2) than pure TGS. In the doping range used, the higher pyroelectric coefficient is traced to a significantly larger spontaneous polarization Ps (∼5 μc/cm2 at room temperature). Tangent δ is below 0.01 over the whole frequency range from 100 Hz to 100 KHz.

Depolarization behavior, and reversible pyroelectricity in lead scandium-tantalate ceramics under DC biases

Abstract The depolarization behavior of ordered and disordered lead scandium-tantalate (PST) ceramics has been studied by Byer-Roundy and Chynoweth method. A sharp decrease of the spontaneous polarization takes place in a narrow temperature range very close to the Curie temperature Tc for the ordered PST materials. For the disordered PST materials, however, the depolarization takes place within a wide temperature range much lower than the temperature of maximum dielectric constant Tm. Evidence of microdomain activities has been observed in disordered materials. The reversible pyroelectric effect is discussed in terms of the micro-macro transition of the domains in disordered PST materials.

Pyroelectric properties of the alanine and arsenic‐doped triglycine sulfate single crystals

Arsenic‐doped triglycine sulfate single crystals show an enhancement in pyroelectric coefficients and the pyroelectric figures of merit p/K and p/√K by a factor of 2.2 over those of pure triglycine sulfate single crystals at the most desirable operating temperature of the pyroelectric sensors, ≂25 °C. The crystals are inexpensive to produce and show useful pyroelectric properties.

Pyroelectric properties of the modified triglycine sulphate (TGS) single crystals

Abstract Several doping substitutions (Li+, Mn+, D+, P+5, As+5) in the TGS structure have been studied and the pyroelectric and dielectric properties measured. In the case of TGS single crystals modified by partial substitution of (P04 −3 and (As04)−3 groups for the (S04)−2. higher pyroelectric coefficients and an enhancement of the pyroelectric material figure of merit (p/K) > 2 x TGS have been observed.

Polarization and depolarization behavior of hot pressed lead lanthanum zirconate titanate ceramics

Abstract Studies have been made of the polarization and depolarization behavior for lead lanthanum zirconate titanate ceramics with zirconia: titania ratio 0.65/0. 35 and La2O3 content from 0.07 to 0.095 (7:65:35 to 9. 5:65:35). Continuity of the dielectric dispersion on cooling unbiased freshly de-aged samples suggests that across this whole composition range for temperatures below the dielectric maxima, there are no macroscopic phase changes. Large remanent polarizations may be built up at low temperatures by cooling under suitable DC bias, but the ceramics will stand off significant bias levels applied at low temperature and remain dispersive. Depoling on heating becomes progressively less abrupt with increasing La2O3 content but is always accomplished well below the temperature of the dielectric maximum. A model involving the ordering and disordering of polar micro-regions under electrical and thermal fields accounts vell for the observed properties.

Pyroelectric properties of a new alanine- and phosphate-substituted triglycine sulphate (ATGSP) crystal

Abstract Phosphorous- and alanine-doped triglycine sulphate (ATGSP) crystals have been grown with partial substitution of H 2 SO 4 with H 3 PO 4 . ATGSP crystals have lower permittivity ( ϵ r ≈ 30) and higher pyroelectric coefficient (6.5 × 10 −4 C/K m 2 ) compared to those of pure TGS. In the doping range used, the higher pyroelectric coefficient is traced to a significantly larger spontaneous polarization P s (≈ 5 μ C/cm 2 at room temperature). Tangent δ is below 0.01 over the whole frequency range from 100 Hz to 100 kHz.

Reversible pyroelectric effect in Pb(Sc1/2Ta1/2)03 ceramics under DC bias

Abstract It has been shown that quenched Pb(Scl/2Ta1/2)03 (PST) disordered ceramics and crystals show diffuse dispersive dielectric properties, while well annealed ordered materials exhibit normal sharp first order transition. The pyroelectric depolarization measurements taken using a Hewlett Packard Model 4140B picoammeter/DC Source under computer controlled heating cycle also have shown different behaviors between disordered and ordered materials In this work pyroelectric measurements by Chynoweth method under DC bias up to 1.8 KV/mm within a temperature range of 70°C around the temperature of maximum dielectric constant have been studied. A very significant enhancement of the pyroelectric signal under DC bias is observed in thermally quenched disordered samples. The largest enhancement of the signal appears at temperatures some degrees below the temperature of maximum dielectric constant The existence of microdomains in disordered materials is believed to be responsible for this new extrinsic component...

Lithium niobate bicrystal

Abstract In studies directed towards improving the basic understanding of the influence of grain boundaries upon the properties of electroceramic materials, studies are being made of artificial planar boundaries created in single domain ferroelectric lithium niobate crystals by thermally bonding carefully polished (001) surfaces. Bonding of “clean” surfaces is accomplished under a uniaxial compressive stress of 106 N/M2 at between 1050 and 1100°C in a time of order 16 to 24 hours. Optical and SEM characterization of the boundary plane is given. New domain features of bicrystal are discussed. In encounter bicrystal, domain shifting through the boundary and domain splitting are observed. Dielectric data for bicrystal are presented.