Dielectric observation of a probably antiferroelectric high pressure phase in the ferroelectric Tris-Sarcosine Calcium Chloride (TSCC)

Dielectric susceptibility and ferroelectric hysteresis measurements on TSCC show that the 2nd-order paraelectric-ferroelectric (PE-FE) phase boundary beginning at (130.8 K, 1 bar) runs with pronounced curvature to (176.8 K, 5.03 kbar), where a new phase of low dielectric susceptibility appears. This phase is hypothesized to be antiferroelectric (AFE) with 3 possible structures: orthorhombic (P2₁2₁2₁, piezoelectric) or monoclinic ($\text{P2}{}_1\text{a}$ or $\text{P2}{}_1\text{n}$, centrosymmetric). The FE-AFE phase boundary was determined down to (81.0 K, 2.60 kbar) and the PE-AFE boundary up to (225.5 K, 6.82 kbar). Both the FE-AFE and PE-AFE transitions are of 1st order over the range studied.     

Temperature and pressure dependence of the elastic property of GeS2 glass

The sound velocities in GeS₂ glass have been measured by means of ultrasonic interferometry as a function of temperature or pressure up to 1.8 kbar. The bulk modulus K_s = 117.6 kbar and shear modulus G = 60.60 kbar were obtained for GeS₂ glass at 15°C and 1 atm. The temperature derivatives of both sound velocities and elastic moduli are negative :

$\text{(}\text{?ν}{}_1\text{?T}\text{)}$

_p =

$\text{?1.54 × 10}{}^{\mathrm{?4}}\text{km}\text{sec}$

°C,

$\text{(}\text{?ν}{}_1\text{?T}\text{)}$

_p =

$\text{?1.27× 10}{}^{\mathrm{?4}}\text{km}\text{sec}$

°C and

$\text{(}\text{?K}{}_{\mathrm{s}}\text{?T}\text{)}$

_p =

$\text{?1.27 × 10}{}^{\mathrm{?2}}\text{kbar}\text{°C}$

,

$\text{(}\text{?G}\text{?T}\text{)}$

_p = ?1.23 × 10^?2 kbar/°C,

$\text{(}\text{?Y}\text{?T}\text{)}$

_p = ?2.93 × 10^?2 their pressure derivatives are positive:

$\text{(}\text{?ν}{}_1\text{?P}\text{)}$

_T = 4.43× 10^?2km/kbar,

$\text{(}\text{?ν}{}_1\text{?P}\text{)}$

_T =

$\text{0.633 × 10}{}^{\mathrm{?2}}\text{km}\text{kbar}$

and (?K_s?P0)_T=6.81,

$\text{(}\text{?G}\text{?P)}{}_{\mathrm{T}}$

= 1.03, (?Y?T_T= 3.57. The Grüneisen parameter, γ_th= 0.298, and the second Grüneisen parameter, δ_s = 3.27, have also been calculated from these data. The elastic behavior of GeS₂ glass has proved to be normal despite the structural similarity among the tetrahedrally coordinated SiO₂, GeO₂ and GeS₂ glasses.     

The pressure dependence of elastic moduli of NiF2 to 10 kbar

At room temperature, the pressure dependence of the elastic stiffness moduli of NiF₂ have been measured by pulse superposition method to 10 kbar. The observed strong decreasing behavior in the modulus $\text{C}{}_{\mathrm{<mtext>s</mtext>}}\text{=}\text{1}\text{2}\text{(C}{}_{11}\text{? C}{}_{12}\text{)}$ is discussed.     

Pressure dependence of dielectric constants of alums

The effect of hydrostatic pressure p on the low frequency dielectric constant ? has been investigated for 31 alums of different composition at 293 K in the pressure range between 0 and 7 kbar. The ?(p)-curves deviate from linearity. For almost all alums with symmetric ions the first-, second-, and third-order pressure derivatives of the dielectric constant obey the following relations:

$\text{(}\text{??}\text{?p}\text{)}{}_{\mathrm{T}}\text{< 0, (}\text{?}{}^2\text{?}\text{?p}{}^2\text{)}{}_{\mathrm{T}}\text{> 0, and (}\text{?}{}^3\text{?}\text{?p}{}^3\text{)}{}_{\mathrm{T}}\text{< 0}$

. The logarithmic volume derivative of the low frequency polarizability, $\text{(}\text{? ln α}\text{? ln V}\text{)}{}_{\mathrm{T}}$, is found to be quasi-invariant also in the isotypic crystal group of alums (Jarman's rule). For the cases, where piezooptical data are available, the optical and infrared contributions to the volume dependence of the polarizability are determined.     

Thermal expansion of LiF at high pressures

Accurate data on the pressure-volume temperature relationship of LiF are presented and compared with recent X-ray measurements by Yagi[1]. Our measurement is a differential length change measurement between a 25 mm long single crystal of LiF and a tungsten carbide standard as previously described by Boehler and Kennedy [2]. A piston-cylinder apparatus with fluid cell arrangement was used up to 32 kbar and 400°C. In spite of the low compressibility of LiF our volume data are accurate within 0.07%. We find a much stronger decline of the thermal expansivity with pressure than Yagi. The values of $\text{α}{}_{\mathrm{v}}\text{· K}{}_{\mathrm{T}}\text{= (}\text{?P}\text{?T}\text{)}{}_{\mathrm{v}}$ remain constant within the uncertainty over our pressure and temperature range.     

Study by brillouin scattering of the C33 constant of thiourea submitted to an electric field

The C₃₃ constant is discontinuous for the lock-in transition at T₁ = 169 K. The variation ΔT₁ of the temperature of transition is a linear function of the applied electric field E and we find $\text{d}\text{T}{}_1\text{d}\text{E}\text{=0.82 deg.cm kV}{}^{\mathrm{?1}}$.Above a mean field E = 10 kV cm^?1 the transition observed for a first heating spreads on several degrees because damages appear in the incommensurate phase and the electric field becomes inhomogeneous.The results obtained at low fields are in very good accordance with the value of $\text{d}\text{T}{}_1\text{d}\text{E}$ calculated from the Clapeyron formula.Taking into account of the incommensurability of the phase above T₁, it can be shown that

$\text{dT}{}_1\text{dE}\text{=}\text{C}\text{2πP}{}_{\mathrm{o}}\text{3}\text{3}\text{?}\text{2}$

The knowledge of the spontaneous polarisation P₀ gives for the Curie constant C = 2.1 × 10³ K in qualitative agreement with the value deduced from measurements of the dielectric constant in the ferroelectric direction.     

High-temperature incommensurate phase and superstructure of LiKSO4

The phase transitions of LiKSO₄ above RT have been investigated by means of X-ray powder diffraction, neutron single-crystal diffraction and thermal analysis. Below ca. 675°C the α phase (most probably isomorphous to α -K₂So₄ with a structure P6₃/mmc) is incommensurately modulated. From the large number of satellite diffractions, a hexagonal triple $\text{k}$ modulation was found with $\text{k}{}_1\text{=}\text{K}\text{a}{}^{\mathrm{☆}}{}_1$ and $\text{K}\text{?}\text{1}\text{2}$. The lock-in transition takes place at 470°C, as $\text{K}$ suddenly becomes $\text{1}\text{2}$. This commensurate phase has the P6₃ symmetry, and is a superstructure of the RT phase. At 439°C the superlattice disappears with the release of latent heat. The dynamical behavior of SO^-2₄ and Li⁺ ions in the higher-temperature phases is discussed. No incommensurate phase is found below RT.     

Lindemann''s criterion and the necessary condition for a melting curve maximum

Dielectric and differential microcalorimetry measurements have been realized on the $\text{Bi}{}_{\mathrm{1?x}}\text{Te}{}_{\mathrm{x}}\text{O}{}_{\mathrm{<mtext>3+x</mtext><mtext>2</mtext>}}$ (0,33 ? x ? 0,50) solid solution. A phase transition has been detected. The variation of the transition temperature with the composition has been determined. The low temperature phase, stable at 20°C, has piezoelectric and non-linear optical properties.     

Defects and diffusion in MnO

Diffusional transport of manganese through MnO scales has been studied at temperatures from 900–1200°C by means of a novel diffusion/evaporation method and by the two-stage oxidation (Rosenburg) method. In the phase field of Mn_1?vO near the MnO₃O₄ phase boundary the manganese self-diffusion coefficient and the concentration of defects is concluded to be proportional to . The concentration of defects increases with decreasing temperature at constant partial pressure of oxygen. In this non-stoichiometry range Mn_1?yO has properties similar to wüstite, Fe_1?yO, and it is concluded that the important cation defects are defect clusters. The results may be explained assuming that the defect clusters consist of four vacancies on octahedral sites and one interstitial on a tetrahedral site. Values for the concentration of defects, the self-diffusion of manganese ions and of the defects have been calculated. For the phase field near the M/MnO phase boundary it is concluded that Mn-interstitials predominate.     

Low temperature specific heats of nearly one-dimensional antiferromagnet: CuCl2·2NC5H5

Transition temperature to LRO state was found at T_N=1.14K for nearly one-dimensional antiferromagnet CuCl₂ · 2NC₅H₅. Intra- and inter-chain exchange constants J and J′ were estimated, $\text{kT}{}_{\mathrm{<mtext>N</mtext>}}\text{J}\text{=0.082}$ and $\text{J′}\text{J}\text{=3×10}{}^{\mathrm{?3}}$, respectively. Comparison with those of TMMC implies highly one-dimensional character.     

Elastic moduli and mode gammas of GaP: Their relationship to those of other isomorphic crystals and the high pressure structural-electrical transition

The transit times of ultrasonic waves associated with piezoelectrically inactive modes have been measured in sulfur-dope, n-type GaP using hydrostatic pressures up to 5 kbar. The velocities and elastic constants of most modes increase linearly with pressure but $\text{C}{}_{\mathrm{S}}\text{=}\text{1}\text{2}\text{(}\text{C}{}_{11}\text{?}\text{C}{}_{12}\text{)}$ decreases slightly. The behavior of the elastic constants and their associated mode gammas are compared to those of other III–V compounds and of Si and Ge. We suggest that the behavior of C_S is related to the occurrence of the structural-electrical transition which occurs at high pressure. A modified Born criterion for lattice stability developed by Demarest $\text{et}$$\text{al}$. is used to explain this relationship. The contribution of thermal dilatation to the temperature dependence of each elastic constant is deduced. Using it and data from the literature we find that the explicit thermal contribution to each elastic constant is significant and in the case of C₁₂ has an anomalous sign.     

Pressure dependence of the magnetic transition fields of the quasi two-dimensional antiferromagnet (C2H5NH3)2 CuCℓ4

Using magnetic susceptibility measurements, we have studied the pressure dependence of the magnetic transition fields of powder samples of antiferromagnetic (C₂H₅NH₃)₂CuC?₄, for hydrostatic pressures up to P ～ 7 kbar. The spin-flop field H₁ decreases linearly with pressure $\text{(}\text{dH}{}_1\text{dP}\text{= ?(20±4)}\text{G}\text{kbar}\text{)}$, while the field corresponding to the paramagnetic transition H₂ shows an increase, ～ 70% for P～7 kbar, that is roughly quadratic with P.     

X-ray compressibility measurements of the graphite intercalates KC8 and KC24

The isothermal compressibilities of pristine graphite and stages 1 and 2 potassium-graphite have been measured at room temperature. Diamond anvil X-ray diffraction techniques were employed to determine the c-axis lattice constant as a function of hydrostatic pressure up to 12 kbar. The compressibilities $\text{k}{}_{\mathrm{c}}\text{?}\text{1}\text{C}{}_{33}$ were found to be (2.73±0.09)×10^-12, (2.13±0.09)×10^-12, (5.3±0.8)×10^-12 and $\text{(1.6±0.2)×10}{}^{-12}\text{cm}{}^2\text{dyn}$ for graphite, KC₈, stage 2 KC₂₄ and stage 3 KC₂₄, respectively. The compressibility of KC₈ was comparable to that of RbC₈ deduced from neutron scattering experiments.     

Light scattering study of dispersion and attenuation of hypersound in adamantane

The Brillouin scattering techniques have been used to measure the velocity dispersion of hypersonic acoustic waves in the “high temperature” disordered cubic phase of adamantane. Shear waves, characteristic of the C₄₄ elastic constant, show no significant dispersion. Longitudinal waves propagating in the (001) plane show strong velocity dispersion. The measures have been performed at the same temperature T = 295.7 K. Using a classical single relaxation time model for the dispersion as a function of frequency at temperature T, the L-mode data have been correctly fitted.The importance of the dispersion $\text{(C}{}_{\mathrm{\infty }}\text{? C}{}_{\mathrm{o}}\text{)}\text{C}{}_0$ for the elastic constants is 20% for C₁₁, 51% for C₁₂ #1% for C₄₄ and ?2.8% for $\text{(C}{}_{11}\text{? C}{}_{12}\text{)}\text{2}$. The fitted relaxation time is τ ? 9 × 10^?11 sec.     

Temperature dependence of the static dielectric constant of Rb2ZnBr4: Solitons in a modulated structure?

The static dielectric constant of Rb₂ZnBr₄ was measured as a function of temperature for a number of different single crystals. In a part of the samples a Curie-Weiss behaviour was observed at the lock-in transition from the incommensurate to the commensurate phase. Besides, in a few samples, a deviation of this behaviour was observed which can be ascribed to the appearance of solitons yielding a soliton density n_s proportional to $\text{(T?T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. At temperatures below T_c two new peaks are observed in the direction of the $\text{a}\text{-}\text{axis}$.     

New high pressure phases of ZrO2 and HfO2

Phase transformations in ZrO₂ and HfO₂ have been investigated in the pressure range between 80 and 300 kbar at about 1000°C in a diamond-anvil press coupled with laser heating. ZrO₂ and HfO₂ have been found to transform to a cotunnite-type structure at pressures greater than 100 and 150 kbar, respectively, and are the first oxides known to adopt this structure. The new polymorphs have the following cell dimensions (Å units) at room temperature and atmospheric pressure:

$\text{ZrO}{}_2\text{:a = 3.328 ± 0.002 HfO}{}_2\text{:a = 3.311 ± 0.002}$

$\text{b = 5.565 ± 0.004 b = 5.550 ± 0.004}$

$\text{c = 6.503 ± 0.005 c = 6.461 ± 0.005.}$

At 1000°C or below, it is suggested that the sequence of high-pressure polymorphism in both ZrO₂ and HfO₂ is baddeleyite → tetragonal → cotunnite with increasing pressure. The polyhedral co-ordination in these polymorphs varies from 7, 8 to 9.     

Raman spectroscopic study of tris-sarcosine calcium chloride in the antiferroelectric phase

The polarized Raman spectra of (CH₃NHCH₂COOH)₃CaCl₂ (TSCC) have been obtained applying hydrostatic pressure in the paraelectric, ferroelectric and in the pressure-induced antiferroelectric phase. The phase transition between the paraelectric or the ferroelectric and the antiferroelectric phase appears to be of first order. No cell doubling could be observed in the antiferroelectric phase. The space group $\text{P2}{}_1\text{a (C}{}^5{}_{\mathrm{2h}}\text{)}$ for TSCC in this phase is compatible with our experimental results. The pressure-dependence of the Raman-active soft mode is discussed qualitatively.     

Pressure spectroscopy of impurity states in GaSb(Se)

Galvanomagnetic effects and Shubnikov-de Haas oscillations are studied in monocrystalline GaSb(Se) samples ($\text{n}{}_{\mathrm{<mtext>se</mtext>}}\text{= 10}{}^{17}\text{?10}{}^{18}\text{cm}{}^{\mathrm{?3}}$) in magnetic fields up to 50 kOe at temperatures 0,07 K ?T?300 K under pressures p?12 kbar. Pressure spectroscopy has been used to determine the density of states in impurity bands and to investigate the anomalies of the transport properties of Γ-electrons near mobility edge ε_c on both metal and insulator sides.     

The concentration dependence of the ferroelectric transition temperature of the solid solution of TSCC and TSCB

The concentration dependence of the ferroelectric transition temperature T_c of single crystals of the solid solution tris-sarcosine calcium chloride_1?x bromide_x is studied experimentally by measurement of the static dielectric constant ?_b and described by the empirical relation $\text{T}{}_{\mathrm{c}}\text{(X) = T}{}_{\mathrm{c}}\text{(0) [1?(X/X}{}_{\mathrm{c}}\text{)]}\text{1}\text{2}$. The Ising model with transverse field and the model of coupled anharmonic oscillators are used to explain the concentration dependence of the transition temperature T_c.     

Defect dominated conductivity in Zn3P2

The electrical resistivity and Hall coefficient of Zn₃P₂ have been measured for single crystal and thin polycrystalline film samples which were annealed over a range of equilibrium vapor compositions and temperatures. The room temperature electrical resistivity of single crystal samples annealed at 573 K varied from approximately 10⁵Ω-cm for single crystals heated in equilibrium with zinc to 10 Ω-cm for those annealed in a phosphorus rich ambient. Hall measurements indicate that a variation in carrier concentration is responsible for these changes. The experimentally observed dependence of carrier concentration [h° ], (cm^?3) on phosphorus pressure is given by [h°] = 1.32 · 10¹⁶ [p(P₄)]^0.13 for samples annealed at 573 K. The experimentally determined pressure dependence is in good agreement with a model based on phosphorus interstitials acting as acceptors. The pressure and temperature dependence of the carrier concentration yield the equilibrium constant K_I for the formation of interstitial phosphorus defects according to the reaction

$\text{1}\text{4}\text{P}{}_4\text{→ P′}{}_{\mathrm{i}}\text{+ h°}$

where

$\text{K}{}_{\mathrm{I}}\text{= 10}{}^{\mathrm{42.4\; \pm \; 2}}\text{cm}{}^{\mathrm{?6}}\text{torr}{}^{0.25}\text{[p(P}{}_4\text{)]}{}^{\mathrm{?0.25}}\text{exp(?1.18}\text{ev}\text{kT}\text{)}$

. The accommodation of phosphorus interstitials is discussed in light of the crystal structure of Zn₃P₂.