Vibrational study of the superprotonic phase transition in the mixed crystal Rb2(HSeO4)(H2PO4)

Raman spectra (10–1200 cm⁻¹) of polycrystalline samples of Rb₂(HSeO₄)(H₂PO₄) were studied at temperatures ranging from 300 to 423 K. An assignment of most of the observed bands is proposed. The first‐order phase transition previously detected at 382 K was characterized as: This superionic‐protonic transition is believed to be governed by librations of the HSe/PO₄²⁻ ion and the A OH (A = Se, P) stretching mode. It corresponds to the weakening of  Se(P) O H˙˙˙ H O Se(P) hydrogen bonds and to the melting of the proton sublattice into a quasi‐liquid state in which the protons and the HSe/PO₄²⁻ ions contribute to the unusually high conductivity. The activation energy that was determined from the plot Δν_1/2 versus temperature for the ν (A OH) band has the same order of magnitude as that determined from conductivity measurements. Copyright © 2006 John Wiley & Sons, Ltd.     

Phase transition in a superprotonic conductor Cs2(HSO4)(H2PO4) induced by water vapor

Phase transitions and thermal history in Cs₂(HSO₄)(H₂PO₄) were analyzed using powder X-ray diffraction method. A high-temperature phase (phase HT), which is a superprotonic phase, was retained on cooling even after 7 days in dry gas atmospheres at 298 K (room-temperature). On the other hand, phase HT did not transform to an original room-temperature phase (phase RT) but to another phase under room temperature and air atmosphere with 60% humidity. The new phase can be the same as the previously reported phase RT2 by means of ¹H NMR [S. Hayashi, M. Mizuno, Solid State Ionics 176 (2005) 745.]. It is revealed that water vapor in atmosphere affects the phase transition, resulting in these large thermal histories.     

Three-dimensionally ordered composite electrode between LiMn2O4 and Li1.5Al0.5Ti1.5(PO4)3

A novel electrode system composed of three-dimensionally ordered macroporous (3DOM) Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) and LiMn₂O₄ was fabricated by the colloidal crystal templating method and sol–gel process. A LATP nanoparticle for the fabrication of 3DOM-LATP was prepared by a sol–gel process. A suspension containing polystyrene (PS) beads and the LATP nanoparticles was filtrated by using a polycarbonate filter to accumulate PS beads and LATP. The accumulated PS beads had a close-packing structure, and the void between PS beads was filled with LATP nanoparticles. 3DOM-LATP was obtained by heat treatment of the accumulated composite. Li–Mn–O sol was injected by a vacuum impregnation process into the macropores of 3DOM-LATP and then was heated to form three-dimensionally ordered composite materials consisting of LiMn₂O₄ and LATP. The formation of the composite between 3DOM-LATP and LiMn₂O₄ were confirmed with scanning electron microscopy and X-ray diffraction method. The prepared composite electrode system exhibited a good electrochemical performance. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Nonlinear dielectric response in the mixed K0.91(NH4)0.09H2PO4 crystal

The influence of bias and variable electric fields on the dielectric response of the K_0.91(NH₄)_0.09H₂PO₄ single crystal has been studied in the vicinity of the ferroelectric phase transition temperature T _C. Below T _C, the nonlinear response is caused mainly by the domain mechanism. This is confirmed, in particular, by observations of chaotic oscillations in a series RLC-circuit containing the studied sample as a capacitor C and excited by a sinusoidal voltage. Peculiarities of the behavior of the dielectric nonlinearity are found near the Curie temperature, which are explained by the emergence of an intermediate heterophase state.     

Preparation of Li1.5Al0.5Ti1.5(PO4)3 solid electrolyte via a co-precipitation method

The co-precipitation method can make the materials react uniformly at molecular level and has the advantages of lower polycrystalline synthesized temperature and shorter sintering time. Therefore, it is expected that the mass production of Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) solid electrolyte would be possible by application of the co-precipitation method for LATP preparation. In this study, an application of the co-precipitation method for a preparation of LATP solid electrolyte is attempted. Crystallized LATP powder is obtained by heating precipitant containing Li, Al, Ti, and PO₄ at 800 °C for 30 min. The LATP bulk sintered pellet is successfully prepared using the crystallized LATP powder by calcinating at 1,050 °C. The cross-sectional SEM images show that many crystal grains exist, and the grains are in good contact with each other, i.e., there is no void space. All diffraction peaks of the pellet are attributed to LATP in XRD pattern. The sintered pellet is obtained by calcinating at 1,050 °C, which is more than 150 °C lower than that of conventional method. The LATP solid electrolyte shows a good conductivity which is 1.4?×?10^?3 S cm^?1 for bulk and 1.5?×?10^?4 S cm^?1 for total conductivities, respectively.     

Amplitude dependences of dielectric permittivity and dielectric losses in a mixed K0.88(NH4)0.12H2PO4 crystal

Amplitude dependences of dielectric permittivity ? and dielectric losses tanδ in K_0.88(NH₄)_0.12H₂PO₄ mixed crystal near the ferroelectric phase transition temperature T _C are investigated. At measurement fields E _～ exceeding some critical value, dependence tanδ(E _～) can be described within a model that includes the depinning of domain walls from point lattice defects. The activation field is found to grow appreciably when approaching T _C from below, due to the presence of nonpolar regions.     

Quasi-reversible superprotonic phase transition in K9H7(SO4)8 · H2O crystals

The heat capacity and the bulk conductivity have been measured in the K₉H₇(SO₄)₈ · H₂O crystal. The hysteresis phenomena have been studied upon superprotonic phase transition. It is revealed that the phase transition is reversible upon thermocycling only for the monohydrate form of the crystal. The exponential temperature dependence of the heat capacity in the supercooled disordered phase exhibits a thermally activated behavior and is determined by the defects responsible for the high conductivity of the crystal.     

Ultrasonic relaxation in Na2Zr1.5Mg0.5 (PO4)3-Al2O3 composite

We present the ultrasonic attenuation dependent on Al₂O₃ concentration at 3 MHz as a function of temperature in Na₂Zr_1.5Mg_0.5(PO₄)₃-Al₂O₃ composite. From the ultrasonic relaxation spectra, we obtained an activation energy and a relaxation strength and then compared to the data obtained from an analysis of frequency-dependent resistivity. The background attenuation at 430 K was also estimated. Owing to these results, we explained an ionic mechanism. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994.     

Synthesis, crystal structure, and spectroscopic study of K0.92(2) Zn0.08(2) H1.92(2) (PO4) (Zn-KDP)

The structure of K0.92₍₂₎ Zn_0.08(2) H_1.92(2) (PO₄) was determined using single-crystal X-ray diffraction. The crystal structure of the Zn-KDP belonged to the tetragonal space group $ \mathrm{I}\overline{4}2\mathrm{d} $ , with cell parameters of a?=?b?=?7.4487(5)?Å and c?=?6.9703(5)?Å, 386.73(5) Å3, Z?=?4, and R?=?0.023. Zn²⁺ ions were used as substitutes for K⁺ ions with hydrogen vacancy. The Zn-KDP single crystals were submitted to further Raman, infrared, and ¹H NMR studies to investigate chemical group functionalisation, possible bonding between the organic and inorganic materials, and partial substitution of K⁺ by Zn²⁺. The latter partial substitution was confirmed by the deviation of IR frequencies for O–H stretching, the variation of IR and Raman frequencies for stretching and bending vibrations ν(PO₄) of H₂PO₄, and the appearance of additional Raman (147, 386 and 481 cm^?1) vibrational bands. Electrical conductivity measurements were performed on polycrystalline pellets of Zn-KDP and pure KDP at room temperatures (RT) of up to 473K. In both cases, a conductivity jump close to 453K was observed, and a stronger increase of conductivity was measured.     

Structural characteristics of olivine Li(Mg0.5Ni0.5)PO4 via TEM analysis

The structural characteristics of olivine-type lithium orthophosphate Li(Mg_0.5Ni_0.5)PO₄ synthesized via solid-state reaction have been studied using X-ray diffraction, ion beam technique, scanning electron microscopy, infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The parent LiNiPO₄ compound can be synthesized in olivine structure without any evidence of secondary phases as impurities. The structural quality of the parent LiNiPO₄ in the absence of secondary component phases resulted in the formation of hexagonal closed packed structure. The olivine analogue compound containing mixed M (M?=?Mg, Ni) cations, Li(Mg_0.5Ni_0.5)PO₄ contained Li₃PO₄ as a second phase upon synthesis, however a carbothermal reduction method produced a single-phase compound. The redox behaviour of carbon-coated Li(Mg_0.5Ni_0.5)PO₄ cathode in aqueous lithium hydroxide as the electrolyte showed reversible lithium intercalation.     

The inelastic neutron scattering study of low temperature lattice dynamics of K1−x (NH4) x H2PO4 mixed crystals

The low-temperature lattice dynamics of K_1–x (NH₄) _x H₂PO₄ mixed crystals have been studied using high-resolution inelastic-neutron-scattering; on powder samples for concentrationsx=0.0; 0.06; 0.1; 0.18; 0.3; 0.6 and 0.9; and on a single crystal forx=0.4. The modes have been assigned and are compared with optical spectroscopy results. It was found that the dynamics of acid protons in the hydrogen-bonds is decoupled from the heavy atom lattice. The displacement vectors for the bending modes are inclined by ca 30° with respect to the hydrogen-bond planes. The influence of ammonium ion concentration on the lattice dynamics has been analysed and the implications for the dipole-glass state are discussed. A vibrational mode at 16.8 meV cannot be distinguished in the glass composition spectra. The inhomogeneous piezoelectric coupling constants in these glasses broaden 16.8 meV band so much that it disappears into the noise. The glass-composition samples show line broadening for the NH₄ whole body motions due to the random hydrogen-bond fields experienced by these ions.     

31P and 2H NMR study of MZr2(PO4)3

²H NMR spectra of (N²H₄)Zr₂(PO₄)₃ and (²H₃O)Zr₂(PO₄)₃ indicate that the cation in these compounds is under going a fast anisotropic reorientation over a wide temperature range 173–373 K. The short T_PH in the ³¹P cross polarisation suggest that diffusion of the cation between M1 and M2 sites is not occuring and hence the motion is likely to be a reorientation within its lattice site.     

Crystal structure,characterisation and vibrational study of a mixed compound Cs0.4Rb0.6H2Po4

Abstract

The crystal structure of Cs_1-x Rb _x H₂PO₄, x = 0.6 (CRDP) which crystallises in space group P2₁/m and is isostructural with the monoclinic phase of CsH₂PO₄ (CDP), has been refined at room temperature using single-crystal X-ray diffractometer data. The cell parameters are a = 4.8183(9)å, b = 6.2671(6) å, c = 7.7620(10)å, β= 108.260(10)°, V = 222.58(5)å³, Z = 2, D_x = 3.009g cm^?3. F(000)=187, T = 298(2)K (room-temperature phase), R = 0.0355 and wR = 0.0949 for 654 observed reflections. CRDP contains two crystallography inequivalent hydrogen bonds in the unit cell. The shorter bond (Ko – o = 2.453(7) A) links the phosphate groups into chains running along the b-axis and the longer bond (Ko – o = 2.488(6) A) which is always ordered, crosslinks the chains to form (001) layers. The phase transitions in the mixed Cs_0.4Rb_0.6H₂PO₄ (CRDP) were characterised by differential scanning calorimetry which shows two anomalies at about 293 and 525 K. The Raman and infrared spectra at room temperature were investigated in the frequency ranges 10–3500 and 200–4000 cm^?1 respectively. An assignment of all the bands is given. The bands are in agreement with the monoclinic room-temperature phase implying high dynamical disorder of the acidic proton O-H s–O hydrogen bond.     

The Mössbauer spectrum of synthetic hureaulite: Fe5 2+(H2O)4(PO4H)2(PO4)2

The crystal structure of synthetic ferrous hureaulite, Fe₅ ²⁺ (H₂O)₄(PO₄H)₂(PO₄)₂, was refined from single-crystal X-ray data. It is monoclinic, space group C2/c, with a=17.487(4), b=9.017(2), c=9.338(2) Å, β=96.27(3)°, V=1463.6(6) Å³, Z=4 and D _calc=3.327 g/cm³. This end member of the hureaulite series was crystallized under distinctly acidic conditions, by a method that gives perfect crystals, large enough for X-ray single crystal studies. The main feature of the hureaulite structure is that it has an equal number of normal (PO₄)³⁺ and acid (PO₄H)²⁺ tetradentate groups. These are centered on Fe²⁺ atoms and share corners with edge-linked octahedra, forming pentamer units. The five Fe²⁺ atoms are distributed on three distinct sites in these units. This can be directly observed in the Mössbauer spectrum at 295 K, which contains three doublets whose relative intensities correspond to the 1:2:2 distributions of crystallographic sites.     

Transient optical absorption of hole polarons in ADP (NH4H2PO4) and KDP (KH2PO4) crystals

A study of transient optical absorption of the ADP (NH₄H₂PO₄) and KDP (KH₂PO₄) nonlinear crystals in the visible and UV spectral regions is reported. Measurements made by absorption optical spectroscopy with nanosecond-time resolution established that the transient optical absorption (TOA) of these crystals originates from optical transitions in the hole A and B radicals and the optical-density relaxation kinetics is rate-controlled by interdefect tunneling recombination, which involves these hole centers and the electronic H⁰ centers representing neutral hydrogen atoms. At 290 K, hole polarons and the H⁰ centers undergo thermally stimulated migration, which is not accompanied by carrier ejection into the conduction or valence band. The slow components of the TOA kinetics with characteristic times from a few tens of milliseconds to a few seconds can be assigned to diffusion-controlled annihilation of hydrogen vacancies associated with impurity or structural defects.     

Structural and electrical characterization of the NASICON-type Li2FeZr(PO4)3 and Li2FeTi(PO4)3 compounds

In order to develop new electrolytes for all-solid-state rocking chair lithium batteries, the NASICON-type compounds Li₂FeZr(PO₄)₃ and Li₂FeTi(PO₄)₃ were investigated by powder X-ray diffraction technique and impedance spectroscopy. Li₂FeZr(PO₄)₃ is orthorhombic Pbna (a=8.706(3), b=8.786(2), c=12.220(5) Å) and Li₂FeTi(PO₄)₃ is orthorhombic Pbca (a=8.557(3), b=8.624(3), c=23.919(6) Å). They show no phase transitions from RT to 800 °C. In the same temperature range logσT vs. 1/T show no slope variations. The activation energies for the ionic conductivity were 0.62 and 0.64 eV for Li₂FeTi(PO₄)₃ and Li₂FeTi(PO₄)₃, respectively. In order to better evaluate the present results they were compared with those of α and β-LiZr₂(PO₄)₃ phases, which were also prepared and characterised. A change of activation energy from 0.47 eV to 1.03 eV was observed in the case of β phase, at about 300 °C; attributed to the β (orthorhombic) ? β′ (monoclinic) phase transition. In the α phase the activation energy 0.47 eV in the temperature range 150 – 850 °C. The Li₂FeZr(PO₄)₃ and Li₂FeTi(PO₄)₃ compounds can be interesting for applications as solid electrolytes in high temperature (>300 °C) lithium batteries.     

Mn5(PO3(OH))2(PO4)2(H2O)4的水热合成和光谱研究

在水热反应条件下合成出具有红磷锰矿结构的Mn5(PO3(OH) ) 2 (PO4 ) 2 (H2 O) 4单晶 ,在X ray单晶结构分析的基础上 ,对其固体紫外可见漫反射光谱、红外光谱、荧光光谱和热重光谱进行了研究。结果表明 ,构成该化合物的PO4 四面体及MnO6 八面体通过共顶点或共棱方式相连接 ,与P ,Mn配位的氧分为 3类 :即端基氧 (Od)、二桥氧 (Ob)和三桥氧 (Oc)。因而在 2 10和 2 5 0nm左右出现了Od→Mn和Ob ,c→Mn的荷移跃迁吸收谱带 ;在 10 0 0～ 110 0cm- 1 处 ,P—O的伸缩振动峰分裂为 3个 ;70 0～ 980cm- 1 处存在 3类Mn—O的伸缩振动。对标题化合物分别采用 2 18和 310nm的光激发 ,分别在 35 4和 4 13nm产生强而尖锐的荧光光谱发射峰 ,表现了很强的光学效应。热重分析表明该化合物在 2 70℃以下结构保持稳定 ,在 2 70～36 0℃范围内失去配位水。量化计算得单点能为 - 4 5 5 8 6 5 95 5 5 1a u ;前线轨道能量HOMO(Alpha) =- 0 2 80 80a u ,LOMO(Alpha) =0 0 15 2 7a u ,能隙为 0 2 96 0 7a u ;HOMO(Beta) =- 0 2 5 919a u ,LOMO(Beta)=0 0 0 10 8a u ,能隙为 0 2 6 0 72a u ;偶极矩为 4 2 0 82Debye。