Lead Hydrogen Phosphate Research Articles

Theoretical Investigation of Ferroelectric and Dielectric Properties of Ferroelectric Lead Hydrogen Arsenate (LHA) Crystal

Ferroelectric crystals show spontaneous electric polarization even in the absence of an electric field. Lead hydrogen arsenate (LHA) is a member of the group of Lead hydrogen phosphate (LHP) type ferroelectric crystals. We have modified earlier two sub-lattice pseudospin model (PLCM) Hamiltonian for LHA crystal. phonon anharmonic terms, four body interaction terms, and extra spin-lattice terms have been added to the model. For the LHA crystal, formulas for Cochran’s frequency, dielectric constant, and loss tangent have been determined using Green’s function approach, and a strong agreement is displayed when comparing our theoretical results to other researchers’ experimental findings.

Thermal dependence of soft mode frequency, dielectric constant, and tangent loss in lead hydrogen phosphate (LHP) crystal

Ferroelectric materials have promising uses in modulators, infrared detectors, data storage devices, and other circuits. The ferroelectric properties in LHP crystallites are investigated theoretically in the study that followed, with some modifications, including the incorporation of fourth and third-orderphonon anharmonic connections, indirect connections, four-body connections, and electric field terms. We will take into account the PLCM model Hamiltonian. Calculations of soft mode frequency, loss tangent, and dielectric constant for said LHP crystal have been computed by using Green's function methodology. The analysis has been done mathematically by putting numerous model values into theoretical expressions that have been established, as well as thermal perturbations of soft mode frequency, Tangent loss (dielectric loss) and dielectric constant have been established. The findings of this study for the LHP crystal are quite well consistent with Negran et al studies of experimental data.

Vibrational spectroscopic study of synthetic analogs of schultenite PbHAsO4–“phosphoschultenite” PbHPO4 solid solution series

Lead hydrogen arsenate PbHAsO4 and lead hydrogen phosphate PbHPO4, which can form a continuous solid solution series, have been extensively studied owing to their ferroelectric properties. PbHAsO4 has also been found to occur in weathered As- and Pb-rich outcrops and historically contaminated soils as a schultenite mineral. Although most ferroelectric studies were of substantial interest more than 30 years ago, the contamination of the Earth’s surface with toxic Pb and As remains a major concern for environmentalists. In this study, six compounds of PbHAsO4–PbHPO4 solid solution series were synthesized from aqueous solutions at ambient conditions. They were subsequently analyzed using Raman and Fourier transform infrared spectroscopy to describe their vibrational characteristics, which should help identify the series members in natural or synthetic samples in further environmental and mineralogical studies. Additionally, powder X-ray diffraction analyses were conducted to investigate the variations in the unit cell parameters along the series. The results showed linear variations in the band positions in both Raman and infrared spectra, which depend on the extent of the isomorphic substitution of (PO4)3− for (AsO4)3−. However, the bands become broader or split as a result of phosphate substitution, making it difficult to correlate the band positions with the molecular composition of an unknown phase. The X-ray diffraction data revealed linear variations of all lattice constants as a function of P. Moreover, a relevant finding of this study is the systematic deviation in the chemical compositions of the synthetic phases from the composition of aqueous solutions from which they precipitated, caused by the preferential incorporation of (AsO4)3− with respect to (PO4)3− into the structure.

Ferroelectric Effect Investigation in Some Lead Hydrogen Phosphate Type Crystal

The formulae to describe ferroelectric effect in PbHPO4 (Lead Hydrogen Phosphate) type crystal are derived. For its simple modified model is used. Simple Green Function formalism is used for derivation numerically thermal variations of normal mode frequency (which brings ferroelectric effect) is obtained anomalous dielectric constant and spontaneous polarization are numerically calculated for PbHSO4 of example for different temperatures. Experimental data are matched with our values. Agreement is found good.

Quantum-Chemical Analysis of the Structural Phase Transition in Quasi–One-Dimensional Ferroelectrics Pb(H/D)PO4

The applicability of the simplest cluster models for semi-quantitative descriptions of the thermodynamics of structural phase transitions in quasi–one-dimensional ferroelectrics is considered. A lead hydrogen phosphate is used as an example. Even such simple models can qualitatively and, in some cases, quantitatively reproduce experimental data.

Effect of the Hydrostatic Pressure on the Thermodynamics of Structural Phase Transition in Quasi-One-Dimensional Ferroelectrics Pb(H/D)PO4: Quantum Chemical Analysis

The change in the structural phase transition thermodynamics of lead hydrogen phosphate (LHP) and lead deuterium phosphate (LDP) depending on the external hydrostatic pressure was studied using the Ising pseudo-spin model taking account of tunneling and long-range effects. The same simplified version of the quantum chemical approach that we proposed for studying these systems at atmospheric pressure was used. The critical transition temperatures Tc were estimated for both systems and the considerable decrease in Tc observed experimentally was explained in each case. The calculations gave an estimate for the width of the barrier in LHP (≈0.35 A); no experimental neutron diffraction value for this barrier is available from the literature.

Temperature Dependence of Soft Mode Frequency, Dielectric Constant and Loss Tangent of Deuterated Lead Hydrogen Phosphate Crystal

Temperature Dependence of Soft Mode Frequency, Dielectric Constant and Loss Tangent of Deuterated Lead Hydrogen Phosphate Crystal

Internal distortion in PO4 3- group of PbHPO4 ferroelectric crystal a structural analysis

A structural phase transition (SPT) mechanism in lead hydrogen phosphate (LHP) based on the neutron structural data is discussed. The contribution of molecular ions to spontaneous polarization (Ps) was calculated using a point charge model. Results indicate that their is a significant contribution in Ps and dipole moment arising out of the distortion of Polar PO4 3- group. Microscopic mechanism of SPT based on molecular distortion (MD) type model can successfully be used in the LHP ferroelectrics.

Proton dynamics in lead hydrogen phosphate crystal

The INS spectra of the powder and oriented single crystals of PbHPO 4 are compared to the infrared and Raman spectra. A detailed band assignment scheme is proposed. There is no evidence for proton tunnelling. The proton dynamics appear very weakly coupled to the heavy atom dynamics.

Growth and characterization of pure and doped lead hydrogen phosphate single crystals in silica gel

AbstractFollowing the chemical reaction method pure and doped lead hydrogen phosphate single crystals were grown in silica gel using different gel density, various concentrations of phosphoric acid, and lead nitrate solutions. As the gel pH plays an important role in the formation of different H3PO4 species in the phosphoric acid system, the pH range in which HPO ions dominate, was considered which in turn in necessary for the growth of lead hydrogen phosphate crystals. Characteristics of these crystals were carried out by infrared spectral analysis and microhardness study.

Kinetics of etching of dislocations in ferroelectric lead hydrogen phosphate and lead nitrate phosphate single crystals

Afin d'etudier les figures d'attaque de dislocation dans des cristaux ferroelectriques de PbHPO 4 et Pb 4 (NO 3 ) 2 (PO 4 )•2H 2 O, emploi de la gravure chimique sur des faces (010) obtenues par croissance et de faces (110) clivees et etude de la vitesse de gravure en fonction de la temperature, ainsi que du processus de dissolution

Nucleation density and electrolytic growth of lead hydrogen phosphate single crystals in silica gels

A detailed study of the variation in nucleation density and growth of lead hydrogen phosphate (LHP), PbHPO4, single crystals as a function concentration of feed solution, gel aging, gel density, gel pH and replenishment programme is presented. While high density and high pH gels produce opaque LHP crystals, good quality transparent LHP single crystals are obtained at low density and low pH gels. It is observed that gel aging considerably reduces the number of nucleation sites. The growth of LHP crystals in silica gels under the influence of an externally applied uniform electric field is also investigated, The implications are discussed.

Pressure dependence of the crystal structure of lead hydrogen phosphate (PbHPO4)

Lead monohydrogen phosphate (PbHPO4) undergoes a ferroelectric phase transition at Tc=310 K at atmospheric pressure. Tc falls to room temperature at a pressure of about 0.125 GPa. The crystal structure of PbHPO4 has been determined by X-ray diffraction at 2.0 and 2.3 GPa and the lattice parameters have been measured at a number of pressures between 0.1 MPa and 3.8 GPa. The unit-cell dimensions change anisotropically under high pressure: the compressibility of b is approximately twice that of a and c. The principal structural changes with pressure are shown to be compression of the distance between the sheets (parallel to the ac plane) of electrostatically interacting Pb2+ and HPO2- ions, and compression of the hydrogen bond connecting the PO4 anions of the neighbouring sheets.

Detection of lattice defects in ferroelectric lead hydrogen phosphate crystals by chemical etching

Single crystals of the LHP up to 7×4×3 mm 3 in size are grown by employing the gel technique. The crystals have found to possess only one perfect cleavage, viz. (110). The nitric acid solution and ammonium perchloric acid at various concentrations are able to reveal satisfactorily the dislocation content of the LHP crystal. Well defined etch pits are traceable on etching of isolated (010) and (110) cleavages of matched pairs revealing the sites of dislocations. Almost all dislocations studied are linear, inclined and parallel. The average density of dislocations is 3×10 2 cm −2 . Low angle boundaries are perferentially attacked during etching

THE DIFFRACTION INTENSITIES OF INCOMPLETELY POLED FERROELECTRIC CRYSTALS

Incomplete poling of ferroelectric crystals has significant effect on their diffraction intensities. In the crystal structure determination, this effect must be taken into account. For lead hydrogen phosphate, appropriate equations are derived to correct this effect. Incorporating this correction in the structure determination of this crystal, a better fit is obtained.

Growth and properties of ferroelectric lead hydrogen phosphate and lead nitrate phosphate single crystals

Ferroelectric lead hydrogen phosphate (LHP) and lead nitrate phosphate (LNP) single crystals are grown together by slow diffusion of lead nitrate by sodium metasilicate gels impregnated with orthophosphoric acid. A brief description of the material preparation, growth procedure and crystal nucleation, is given. Bright and transparent prismatic LHP crystals up to 7 × 4 × 3 mm 3 and LNP crystals up to 12 × 6 × 3 mm 3 in size are obtained. It is observed that the growth rate of the LNP crystals is faster than that of the LHP crystals. Results obtained on characterization of these two crystals chemical, and on analysis, X-ray diffraction, EDAX, etc. are reported. The microhardness and Young modulus of these crystals are determined. The average density of dislocations has been determined by employing the chemical etching technique and found to be 3 × 10 2 cm -2 in LHP and 7 × 10 2 cm -2 in LNP crystals. The implications are discussed.

A comparative study of gel grown and space grown lead hydrogen phosphate crystals

Lead hydrogen phosphate (LHP) and lead nitrophosphate (LNP) crystals have been grown by counterdiffusion of lead nitrate and phosphoric acid solutions either in a gelled medium or in a free medium under the reduced gravity environment of Spacelab. Characterization of grown crystals allows to conclude that diffusive regimes are obtained in both xases. Dielectric measurements reveal significant differences which can be correlated with the crystalline quality.

Vickers micromechanical indentation and compression testing of ferroelectric lead hydrogen phosphate single crystals

Ferroelectric crystals of lead hydrogen phosphate (LHP) have been synthesized using the controlled diffusion of lead nitrate into a set gel containing orthophosphoric acid. The variation in the microhardness of LHP crystals has been determined using a Vickers microhardness indentor. The effects of annealing and quenching on the mechanical properties of these crystals have been studied. It is observed that (i) the microhardness of the crystals depends on the applied load and is independent of the duration of loading, (ii) irrespective of the relative orientation of the indentor and the crystal, the median vents initiate at the sharp indentation edges, and (iii) maximum plasticity is observed in quenched crystals. The mechanical behaviour of the crystals has been studied using an Instron compression testing unit. A large anisotropy is observed from experiments on the breaking strength of the crystals and the implications are discussed.

Magnetic susceptibility measurements of LHP and LNP crystals

Ferroelectric single crystals such as lead hydrogen phosphate (LHP) and dihydrated lead nitrate phosphate (LNP) have been derived from the diffusion of lead nitrate into the set gel containing orthophosphoric acid. By employing Faraday’s Gouy balance technique, the magnetic susceptibilities of LHP and LNP have been determined. It has been observed that (i) the gram and molar susceptibilities are independent of magnetic field, (ii)χ M of LNP materials are greater than that of LHP materials and (iii) the positive values of magnetic susceptibilities suggest that LHP and LNP are paramagnetic materials.

Dielectric properties of ferroelectric lead hydrogen phosphate single crystals

AbstractThe ferroelectric lead hydrogen phosphate (LHP) single crystals have been grown by employing the gel technique. The controlled reaction between lead nitrate and orthophosphoric acid solutions by diffusion process in gel medium has been used. The dielectric constant (ϵ′) and the dielectric loss (ϵ″) have been measured for the first time as a function of frequency in the range 102 to 104 Hz. They have also been determined as a function of temperatures in the range 300 to 680 K. The polarisation effect contributing to the dielectric constant has been studied. It has been observed that the mechanism of the dielectric behaviour is different in the lower and higher temperatur and frequency ranges. The activation energy of the oscillators has been calculated and found to be 1.12 eV. Attempt has been made to draw some qualitative conclusions, taking in view, the existing theories of various kinds of polarization and implications have been discussed.