Spectroscopic manifestation for the isotopic substitution in potassium dihydrogen phosphate

The normal vibration spectra of potassium dihydrogen phosphate (KDP) and its deuterated analogue K(D_xH_1−x)PO₄ (DKDP), which arise mainly from internal vibrations of PO₄ tetrahedrons, were recorded by the micro-Raman spectrophotometer system. The four characteristic internal vibration modes of the (H/D)₂PO₄ anion in (D)KDP are assigned by comparing their polarized Raman spectra. The bands of H-vibrations recorded in the FTIR spectra, which have been interpreted as the O–H/D stretching modes, the in-plane bending, and the out-of-plane bending vibrations, are tentatively assigned as well. The frequency ratio of the O–H/D modes due to the hydrogen or deuterium is 1/1.37, which coincides with the ratio of square root of the reduced mass of O–H and O–D.     

-NMRC-NMR study on κ-(BEDT-TTF)2X

The electronic state of the κ phase family of BEDT-TTF compounds, κ-(BEDT-TTF)₂X [X = Cu(NCS)₂, Cu[N(CN)₂]Br and Cu[N(CN)₂]Cl], has been investigated by -NMR¹³C-NMR as well as H-NMR.¹-NMR. The ¹³C isotope was substituted selectively into the central double bonded carbon sites of BEDT-TTF. The ¹³C nuclear spin-lattice relaxation rate and line spectra have been measured for the Cu(NCS)₂ and Cu[N(CN)₂]Br salts. The Knight shift evaluated from the the width of the spectra of the powdered samples is temperature-insensitive and scaled to the uniform susceptibility. However, the relaxation rate, T₁⁻¹, does not obey the Korringa law but exhibits anomalous temperature dependence with a peak formation around 50 K. The absolute value of T₁⁻¹ is in excess of the Korringa relation. These behaviors are considered to come from strong aniferromagnetic spin fluctuation with finite wave vector, which is suppressed below 50 K. On the other hand, the H¹ NMR and magnetization measurements gave an unambiguous evidence for antiferromagnetic transition with spin canting at 25 K in κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl. The κ phase family, situated in the vicinity of metal-insulator and magnetic transitions, is characterized by strong electron correlations.     

Acoustic investigations of the ZrV2–H system

Elastic modulus and internal friction of the ZrV₂H_x system have been measured by the method of low-frequency acoustics (1 kHz) in a wide range of hydrogen concentrations (0 ≤ x ≤ 6) and temperatures (65 K < T < 300 K). It is established that an increase of the hydrogen concentration shifts the structural phase transformation from the rhombohedral to the cubic phase of the ZrV₂ compound towards high temperatures and leads to its suppression. An anomaly of the elastic modulus in the concentration range 0.7 < x ≤ 6 with a corresponding peak of the internal friction was detected at a temperature of 200 K, characteristic of the phase transition. The relaxation peak of the internal friction observed above 200 K is caused by dissipation of elastic energy on interphase boundaries.     

Hydrogen in alkali-metal-graphite intercalation compounds

The sorption and desorption of hydrogen by alkali-metal-graphite intercalation compounds (AGICs), MC₈ and MC₂₄ (M = K, Rb and Cs), were studied by the constant-volume closed method and mass-analyzed thermal desorption spectroscopy. Three forms of hydrogen were detected in KC₈H_x and KC₂₄H_x, while two forms in RbC₈H_x and one form in RbC₂₄H_x were detected. The energy diagrams for the systems composed of AGICs and hydrogen demonstrate that the type of alkali metal intercalated in graphite and the stage structure of AGICs have greater influence on the absorption process than on the adsorption process of hydrogen.     

The NMR properties of Yb nucleus in AYbI3 (A: K, Rb, Cs) in solid state

The powder and magic-angle spinning (MAS) experiments on ¹⁷¹Yb in AYbI₃ (A: K, Rb, Cs) are reported. The NMR parameters, such as the principal components of the chemical shielding tensor (δ₁₁, δ₂₂, δ₃₃), the spin-lattice relaxation time and the parallel and perpendicular components (T₁, T₁, T₁) are determined in solid state and the transverse relaxation time was obtained from the natural line width. The local symmetry of Yb was discussed according to the spectra.     

Structural studies in lead fluorogermanate and fluorosilicate glasses

We report the results of structural studies by means of Eu³⁺ fluorescence line narrowing techniques in the binary systems PbF₂-GeO₂ and PbF₂-SiO₂. Several features characteristic of the europium fluorescence in lead glasses are put forward. The absence of selectively excited emission at room temperature demonstrates an unusually large homogeneous broadening of the electronic levels. A relative increase in the ⁵D₀ → ⁷F₁ (magnetic dipole) with respect to the ⁶D₀ → ⁷F₂ (electric dipole) transition is observed with time-resolved. detection. This effect shows that accidental coincidences of ⁵D₀ → ⁷F₀ energies and ⁷F₁ splitting do occur between europium sites differing only by their ⁶D₀ lifetimes and magnetic dipole: electric dipolar relative intensities. The general characteristics are interpreted with oxygen neighbours for Eu³⁺ rather than fluorine ions. The crystal field strength expressed as N_v = [∑_k,a (B_g^k)² × 4π/(2k + 1)]^1/2 (limited to k=2 parameters) is slightly higher in the germanate than in the silicate matrix.     

Growth of single crystals of Hg(BrxI1−x)2 and their detection capability

Hg(Br_xI_1−x)₂ crystals were grown by the Bridgman method for 0.2 < x < 1.0. They were tested for potential implementation as X- and γ-ray detectors at room temperature. ²⁴¹Am and ⁵⁵Fe were used as radioactive sources. From the corresponding energy spectra, it is evident that crystals with x = 0.2 show enhanced resolution at low energies (below 200 keV), competing those fabricated from HgI₂ and CdTe. Crystals with higher x's were of lower resolution.     

High pressure spectroscopy of Pr in LiNbO3

Absorption, emission, and luminescence excitation spectra of the LiNbO₃ crystal doped with 0.5% Pr³⁺ and 0.8% Yb³⁺ are presented. Additionally the photoluminescence spectra at high pressure have been measured. Hydrostatic pressures up to 135 kbar were applied with a diamond anvil cell. Absorption of the Pr³⁺:LiNbO₃ crystal is characterized by the strong threshold at about 400 nm, related to the band-to band-transitions and the sharp structure in the visible region attributed to the transitions to ³P_J and ¹D₂ levels of Pr³⁺ ion. After the 488 nm excitation the yellow emission related to the ¹D₂→³H_J transition of Pr³⁺ have been observed when the ³P₀ emission has not been detected. The excitation spectra of the ¹D₂ luminescence consist of the sharp lines related to the ³H₄→³P_J (J=0, 1, 2) transitions and two broad bands peaked at 340 and 400 nm related probably to the bound exciton. The ¹D₂→³H_J emission shifts with pressure toward the lower energies with the rate of −2.4 cm⁻¹ kbar⁻¹. Additionally, for higher pressures the ¹D₂ emission is considerably quenched. This is explained as being due to the decrease of the energy of the bound exciton with pressure which results in the higher nonradiative depopulation rate of the ¹D₂ state.     

Crystal fields in (La1−xGdx)OCl:Eu solid solutions

The formation of cation solid solution in the (La_1−xGd_x)OCl:Eu³⁺ (0≤x_Gd≤1; Δx_Gd=0.1) series was studied by photoluminescence spectroscopy. The luminescence from the ⁵D_0–2 to the ⁷F_0–4 levels of the Eu³⁺ ion in the (La_1−xGd_x)OCl series was recorded at 77 K by using argon ion laser excitation (457.9 nm). The interpretation of the spectra according to the C_4v site symmetry of the Eu³⁺ ion in the tetragonal PbFCl-type structure yielded nearly complete sets (18 to 19 levels) for the ⁷F_0–4 levels. Simulations of the Stark level schemes were carried out with the aid of a phenomenological c.f. theory utilizing the five non-zero c.f. B_q^k parameters (B₀², B₀⁴, B₄⁴, B₀⁶ and B₄⁶) allowed for the C_4v site symmetry. By using the calculated c.f. parameter sets a quantitative measure was obtained to monitor the formation of cation solid solutions. The strength of the c.f. effect was estimated with the c.f. strength parameters S and S^k (k=2, 4 and 6). The c.f. parameter sets reproduced the experimental ⁷F_J (J=0–4) energy level schemes with the rms deviations between 4 and 11 cm⁻¹. The individual parameters as well as the c.f. strength parameters were found to evolve in a smooth manner indicating complete solid solubility in the (La_1−xGd_x)OCl series. Some local distortions from the C_4v symmetry — probably of long range—leading to the splitting of the ⁷F₁ doubly degenerate E level were observed, however.     

Spectroscopy, magnetism and non-radiative processes in heteronuclear Cu:Pr squarate; [Pr2Cu(C4O4)4(H2O)16]·2H2O

In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystal, where squarate anions participate as bridging ligands between metal ions.

The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A_1g→E_u) and π–π*(A_1g→E_g) ligand transitions. In visible and IR regions, t_2g–e_g of copper Cu(II) as well as ³H₄→³P_J, ¹D₂, ¹G₄, ³F_J, ³H₆ Pr(III) transitions at 293 and 4 K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of ³H₄→¹G₄ transition is probably due to the intensity borrowing from the Cu (II) d–d transition.

The ³P₀ and ¹D₂ emission of Pr(III) in the [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystals is quenched even at 77 K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by e_g levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7 K temperature range and are discussed in relation to the structure.

Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown.     

Temporal evolution of the nanostructure of Al(Sc,Zr) alloys: Part II-coarsening of Al3(Sc1−xZrx) precipitates

The coarsening behavior of four Al(Sc,Zr) alloys containing small volume fractions (<0.01) of Al₃(Sc_1−xZr_x) (L1₂) precipitates was investigated employing conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The activation energies for diffusion-limited coarsening were obtained employing the Umantsev–Olson–Kuehmann–Voorhees (UOKV) model for multi-component alloys. The addition of Zr is shown to retard significantly the coarsening rate and stabilize precipitate morphologies. HREM of Al(Sc,Zr) alloys aged at 300 °C reveals Al₃(Sc_1−xZr_x) precipitates with sharp facets parallel to {1 0 0} and {1 1 0} planes. Coarsening of Al-0.07 Sc-0.019 Zr at.%, Al-0.06 Sc-0.005 Zr at.% and Al-0.09 Sc-0.047 Zr at.% alloys is shown to be controlled by volume diffusion of Zr atoms, while coarsening of Al-0.14 Sc-0.012 Zr at.% is controlled by volume diffusion of Sc atoms.     

Properties of ytterbium and neodymium doped alkali metal yttrium double phosphates of the M3Y1−xLnx(PO4)2 type

The spectroscopic behaviour of the Nd³⁺ and Yb³⁺ doped alkaline metal yttrium double phosphates, M₃Y_1−xLn_x(PO₄)₂ (M=Na, Rb; x=0.01–0.3) were studied for both powder and single crystal samples. The high resolution absorption and emission spectra were measured in the visible and IR regions. Spectral changes with the Nd³⁺ and Yb³⁺ concentration were interpreted. The absorption strengths of the 4f–4f transitions were analysed and used to assess the structural modifications of the two double phosphates. Based on the 4 K absorption spectra the number of metal sites occupied by the dopants was investigated.

Strong emission from Na₃Y_1−xNd_x(PO₄)₂ involving the ⁴F_3/2→⁴I_9/2,⁴I_11/2,⁴I_13/2,⁴I_15/2 transitions were observed whereas the corresponding emission from the rubidium phosphate was presumably quenched by multiphonon processes due to the water molecules absorbed in the channel-like structure.

The IR spectra were used to assign the vibronic components of the electronic transitions. The Yb³⁺ emission bands were broadened depending on the Yb³⁺ concentration (1–10 mol%). The tentative energy level scheme of the ground and excited ²F_J (J=7/2, 5/2) levels was described.     

Subject Index

Luminescence, luminescence excitation and electronic absorption spectra of europium salts of isomeric lutidine N-oxide derivatives were studied at 293 and 77 K. The role of radiative and non-radiative processes in emission intensity is discussed. The absorption transitions to the ³F_J, ⁵D_J, ⁵L_J and ⁵G_J levels and emissions from the ⁵D₀ and ⁵D₂ levels were detected. The role of CT transition inside the ligand and its influence on the LMCT transition is analysed. The co-ordinating function of the lutidine N-oxide group is discussed using IR spectroscopy.     

Dependence of dielectric properties of manganese-doped strontium titanate ceramics on sintering atmosphere

It is shown in this paper that the microscopic mechanism of the dielectric relaxation in Mn-doped strontium titanate (SrTiO₃–ST) ceramics is associated with the off-center displacement of ions. This was accomplished by studying the dielectric properties and electron spin resonance spectroscopy in combination with X-ray powder diffractometry and scanning electron microscopy techniques in Sr_1−xMn_xTiO₃ ceramic samples sintered in different atmospheres (air, oxygen and nitrogen) at 1500 °C. First, it is shown that manganese is incorporated into the perovskite lattice of ST, preferably as Mn²⁺ at Sr sites. However, a small amount of Mn⁴⁺ at Ti sites is also observed when fired in air or oxygen flow. The concentration of is the highest for sintering in oxygen, but firing in a reducing atmosphere (nitrogen) results solely in the incorporation of Mn²⁺ at Sr sites. Correspondingly, the dielectric relaxation observed in Sr_1−xMn_xTiO₃ markedly increases in intensity and slightly shifts towards a higher temperature for ceramics sintered in nitrogen compared with those fired in air or oxygen. All these facts are consistent with a suggestion that the off-center displacement of Mn²⁺ ions at the Sr sites of the highly polarizable ST lattice is the source of the observed relaxation behavior.     

TDPAC study of the Hf-doped LaNi5-hydrogen system

The dependence of the electric field gradients (EFGs) in the Hf-doped LaNi₅-hydrogen system, as a function of hydrogen composition ratio (X), has been investigated in the range 0≤X≤5.7 using the Time Differential Perturbed Angular Correlation (TDPAC) technique. The TDPAC spectrum of LaNi₅ was fitted with a single EFG, while two EFGs were needed to fit the LaNi₅H_x spectra. The first EFG was similar to the one found in metallic LaNi₅ and the second one was interpreted as related to those probe atoms located in the basal plane next to hydrogen interstitial sites located in the same plane. The relative fraction of the probe atoms experiencing these EFGs is dependent on the relative occupation of hydrogen in these sites.     

Relaxational lattice dynamics in La2−xSrxCuO4 and possible connection with the stripes in cuprate superconductors

The dynamic Young’s modulus of La_2−xSr_xCuO₄ (x=0.022, 0.032) has been measured down to 1.5 K, in order to see the effect of doping on the intrinsic lattice fluctuations found in stoichiometric La₂CuO₄, and identified with tilting relaxation modes of the O octahedra. The relaxation process occurring at lower temperature drastically shifts to still lower temperatures, implying an enhancement of the corresponding relaxation rate with doping. This observation is in accordance with the hypothesis of tunnelling-driven pseudodiffusive switching of the octahedra between minima of a multiwell potential, with the distances and barriers between minima decreasing upon doping. The present measurements, together with a model of the excitations of a planar array of octahedra, provide a possible scenario for the evolution of the stripe phase in the cuprate superconductors at low doping.     

Hydriding kinetics of the La1.5Ni0.5Mg17–H system prepared by hydriding combustion synthesis

An experimental investigation of the hydrogen absorption rate in the two-phase (–β) region of La_1.5Ni_0.5Mg₁₇ powder under the condition of various pressures and temperatures is presented. The results are well interpreted using the Jander diffusion model, [1−(1−ξ)^1/3]²=k(T,P)t, which suggests that the rate-controlling step of hydrogen absorption in La_1.5Ni_0.5Mg₁₇ is three-dimensional diffusion. An apparent activation energy for such diffusion process of 90±1 kJ/mol H₂ has been obtained from the absorption data.     

Synthesis and characterization of proton conducting Sr(Ce1−xZrx)0.95Yb0.05O3−δ by the citrate method

The citrate method was used to synthesize Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ (x = 0.1, 0.2, 0.3, 0.4) and to avoid the drawbacks of the conventional solid state reaction method. The products were characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe X-ray microanalyzer (EPMA). The results indicate that the citrate method is an advantageous route in producing Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ materials. Sr(Ce_0.9Zr_0.1)_0.95Yb_0.05O_3−δ powders are composed of nanoscaled crystallites with the average grain size in the range of 60–70 nm. Single phase is confirmed over the whole x range. In addition, chemical stability against CO₂ and electrical conduction behavior of the sintered Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ ceramics were investigated. The chemical stability of the ceramics against CO₂ is certified to increase with the increase in zirconium content. Impedance spectroscopy was used to study the electrical conduction behavior of Sr(Ce_0.9Zr_0.1)_0.95Yb_0.05O_3−δ ceramic.     

Iodine-doped bridged phthalocyaninatoiron(II) and -ruthenium(II) compounds

Phthalocyaninatoiron(II) and -ruthenium(II) compounds [R_mPcML]n(M = Fe, Ru) with different bridging ligands L = 1,4-diisocyanobenzene (1,4-dib), 1,4-dicyanobenzene (dcb), 4,4′-diisocyanobiphenyl (dibph) and 4,4′-bipyridylacetylene (bpyac), 2,3,5,6-tetramethyldiisocyanobenzene (Me₄dib), 2,3,5,6-tetrachlorodiisocyanobenzene (Cl₄dib) and 1,3-diisocyanobenzene (1,3-dib) are reacted with iodine using different doping procedures. Except for the perchlorocomplexes 8a and 17a, stable compounds [R_mPcMLI_y]_n are formed, which were characterized by thermogravimetric measurements, infrared, resonance-Raman and ⁵⁷Fe-Mössbauer spectroscopy. An increasing dopant level of iodine causes a continuous increase in electronic conductivity of the compounds [R_mPcMLI_y]_n, which, in spite of their comparatively large inter-ring distances, exhibit room-temperature powder conductivities in the range σ_RT = 10⁻² -10⁻¹ S/cm.     

Optical constants of polyacetylene

Optical constants of neat cis- and trans-(CH)_x and (CD)_x films are determined by measuring infrared, visible and ultraviolet spectra of the film and its thickness directly. The absorption coefficient of cis-(CH)_x at the absorption maximum 18 500 cm⁻¹ was (1.5 ± 0.1) × 10⁵ cm⁻¹ and that of trans-(CH)_x at 15 500 cm⁻¹ was 1.5 × 10⁵ cm⁻¹. The same values as those of (CH)_x were obtained for (CD)_x. The refractive indices and dielectric constants of cis- and trans-(CH)_x were calculated based on absorptionvspectral data.