Effect of Synthesis Conditions on the Lithium Nonstoichiometry and Properties of La2/3 – x Li3x □4/3 – 2x M2O6 (M = Nb, Ta) Perovskite-like Solid Solutions

The effects of the nominal composition and synthesis conditions on the lithium nonstoichiometry of La_{2/3 – x} Li_{3x 4/3 – 2x} Nb₂O₆ (I) and La_{2/3 – x} Li_{3x 4/3 – 2x} Ta₂O₆ (II) solid solutions are studied. The results demonstrate that lithium losses can be reduced from 26–30 to 14–15 mol % in system I and from 15 to 4 mol % in system II. It is shown that the disturbance of electroneutrality caused by Li nonstoichiometry in the solid solutions is eliminated via the formation of oxygen vacancies in positions O(1) (1f: 1/2 1/2 0) and O(2) (1h: 1/2 1/2 1/2) of the cation-deficient perovskite structure. The optimal lithium ion conductivity is offered by solid solutions with /3x 2.6 and x 0.136–0.143.     

Photoconductivity in Oxygen Deficient La0.7 Pbx □0.3 ? x MnO3 ? δ Thin Films Prepared by Chemical Route

We report the influence of light irradiation on the electrical properties of oxygen deficient La_0.7Pb_{x 0.3 – x} MnO_{3 –} thin films with (x = 0.1) and without (x = 0.3) cation vacancies (noted by ). Transient photoconductivity and photoinduced insulator–metal transition occurs at low temperatures in these thin films. Introducing cation vacancies does not increase the Mn⁴⁺/Mn³⁺ ratio but creates a sheared structure that decreases the oxygen content and can explain our transport and photoconductivity results.     

Low-temperature synthesis and characterization of ceria-based oxide ion conductors

Solid solutions of the general formula Ce_1–x Ln _x O_2–x/2x/2 (Ln = lanthanide (III) and = anion vacancy), were prepared by a novel sol-gel route. These materials were characterized by powder diffraction and scanning electron microscopy. The gels formed on sol evaporation were found to be solid solutions with the fluorite structure and a crystallite size of approximately 6 nm. This is the lowest temperature of formation to date. The gels densified readily at 700 °C and the lattice parameter of these materials was found to be directly proportional to the ionic radius of the dopant.     

Structural and Transport Properties of La2/3 – x Li3x □4/3 – 2x Ta2O6 Perovskite-Like Solid Solutions

The homogeneity range of La_2/3–x Li_{3x 4/3 – 2x} Ta₂O₆ perovskite-like solid solutions was determined. The transport properties of the La_2/3–x Li_{3x 4/3 – 2x} Ta₂O₆ oxides were shown to correlate with their lattice parameters and composition. Lithium-doped lanthanum metatantalate with an orthorhombically distorted perovskite-like structure is a good solid electrolyte with high lithium ion conductivity.     

Preparation, Structure, and Electrical Conductivity of La(Ga,Mn)O3 Ceramics

(La_0.90.1)(Ga_{1 – x} Mn _x )O _y ( = vacancy;x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) perovskite solid solutions are prepared by solid-state reactions and characterized by x-ray diffraction, electron microscopy, and dielectric spectroscopy. The solid solutions have a rhombohedral structure over the entire composition range. Mn substitution leads to a transition from ionic hopping conduction, with a linear variation of log (T) with 1/T, to ionic–electronic conduction. The unit-cell volume and conductivity of the solid solutions are shown to correlate with their tolerance factor.     

Synthesis of titanium nitride by a spark-discharge method in liquid ammonia

Titanium nitride powders were synthesized by the spark-discharge method in liquid ammonia at — 78 to 130 °C and 3.5–10.5 kV discharge voltage using titanium pellets as the starting materials. Titanium nitride possessing nitrogen defect, TiN_1–x (x0.5), was obtained as the main product, together with small amounts of -Ti alloyed with nitrogen. The increase in temperature of the liquid ammonia resulted in an increase in the titanium nitride content in the product but a decrease in the powder production rate. By calcining the mixed powders of TiN_1–x and -Ti in a nitrogen atmosphere around 1200 °C, stoichiometric TiN was obtained as single phase.     

IR Spectra of La1.85Sr0.15Cu1?xMxO4?δ(M = Zn, Ni, Mg)

Polycrystalline samples La_1.85Sr_0.15Cu_1–xZn_xO_4– (0 x 0.3), La_1.85Sr_0.15Cu_1–xNi_xO_4– (0 x 0.3), and La_1.85Sr_0.15Cu_1–xMg_xO_4– (0 x 0.3) were synthesized by the solid-state reaction method. The crystal structure and phonon vibration were investigated by means of X-ray diffraction (XRD) and infrared spectrum. Zn, Ni, and Mg doping results in the lattice parameter c decreasing and a (b) increasing. The change of the phonon modes around 504 cm^–1 and 681 cm^–1 can be satisfactorily interpreted in terms of the change of the crystal structure and the itinerant nature of charge carrier in CuO₂ sheet. The relation between the structure and phonon vibration is discussed.     

Oxygen Stoichiometry and Phase Transitions of SrCo1– xFexO3 – δ

The oxygen stoichiometry of SrCo_{1 – x} Fe _x O_{3 –} (0.1 x 0.9) solid solutions was determined by solid-electrolyte coulometry as a function of temperature (20–1000°C) and oxygen partial pressure (1–100 Pa). The results, together with X-ray diffraction studies between 400 and 900°C, indicated a sequence of phase transitions: perovskite brownmillerite high-temperature perovskite. The composition stability region of the parent perovskite structure was shown to be 0.2 <x 1.0. The Co-rich samples (x 0.2) consisted of perovskite and hexagonal phases.     

Nuclear ferromagnetic ordering of141Pr in the diluted Van Vleck paramagnets Pr1−x Y x Ni5

We report on the first investigation of the effect of magnetic dilution on nuclear magnetic spin interactions in metals; we studied this effect in the diluted Van Vleck paramagnets Pr_1–xY_xNi₅. In addition, we investigated the electronic magnetic properties of these intermetallic compounds. For this purpose, we have measured the nuclear and electronic susceptibilities of Pr_1–xY_xNi5 with x = 0 to 0.2 at 50K T 8 mK and at 2.2 K T 300 K. We observe a linear decrease of the electronic Van Vleck susceptibility and of the hyperfine enhancement factor by 13% (per mole Pr³⁺). The hyperfine-enhanced nuclear susceptibility decreases by about a factor of three when going fromx = 0 tox = 0.2. The samples show nuclear ferromagnetic transitions of¹⁴¹Pr with nuclear Curie temperatures T_c decreasing from 370 K to 100 K and Weiss temperatures decreasing from 218 K to 13 K in this concentration range. These data are compared with the results of mean-field calculations. In addition, we report on measurements of the nuclear spin relaxation time of these compounds, for which we find values of a few msec at millikelvin temperatures and a critical speeding-up at T_c. Our data give hints that for x > 0.2 the character of the nuclear magnetic transition may change, possibly to a nuclear spin glass freezing.     

Effect of gamma irradiation and silver doping on YBCO superconductor

The effect of -irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)_1–xAg _x systematically increase by about 2 K with an increase of Ag content up tox=0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up tox=0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)_1.96Ag_0.04 were irradiated with-rays up to an integrated-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with -irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T _c supconductor YBCO is quite sensitive to-irradiation but drastic lattice expansion does not occur up to a-dose of 77 MR.     

Ionic conductivity and crystal structure relationships in Ti/Cu substituted Bi4V2O11

Crystal structure and oxide ion conductivity of a series of Ti and Ti-Cu double substituted Bi₄V₂O₁₁ compounds, Bi₂V_(1–x)Ti _x O_(11–x)/2 (0.085 x 0.15), and Bi₂V_0.9Cu_(0.1–x)TixO_5.35+x (0 x 0.1), were investigated using X-ray powder diffraction and ac impedance spectroscopy in the temperature and frequency range of 100–700°C and 10^–2–10⁷ Hz, respectively.Structural phase transitions, and , occur as a function of composition in Ti substituted compounds for which the is evidenced to be stable at room temperature when x exceeds 0.125. For all Ti-Cu double substituted compounds studied, the room temperature phase was identified to be phase.The required amount of Ti for phase stabilization at room temperature was significantly reduced and the conductivity improved when Cu substituted a part of Ti. Therefore, for the Bi₂V_0.9Cu_(0.1–x)Ti _x O_5.35+x (0 x 0.075) compounds the ionic conductivity increased and activation energy decreased with decreasing x. At low temperature, the highest ion conductivity was obtained for Bi₂V_0.9Cu_0.1O_5.35. At high temperature (T>500°C), a different behavior was observed. The total conductivity increased at first with decreasing x values down to x = 0.05 and then decreased. The maximum conductivity was obtained for Bi₂V_0.9Cu_0.05Ti_0.05O_5.4, and the activation energy decreased with decreasing x values, such as what happened at low temperature.     

Mechanical relaxation of 4 wt% Y2O3-ZrO2 tetragonal single crystals

The mechanical relaxation was examined by a resonance piezoelectric method for a 3.5 wt % Y₂O₃-ZrO₂ polycrystal and 4 wt% Y₂O₃-ZrO₂ tetragonal single crystals with orientations in the 100 and 111 directions. The relaxation was observed for the 111-oriented crystal, but not for the 100-crystal. The results indicated that the relaxation was active only for the elastic compliance, S₄₄, and inactive for (s ₁₁–s ₁₂). The amplitude of the anelastic relaxation measured for the polycrystalline and the 111-crystal body was 4.2 × 10^–12 m²N^–1 and 6.7×10^–12 m² N^–1, respectively. An observed broad relaxation peak suggested that complex processes exist even in single crystals.     

Physicochemical Properties of R1 – xBaxMnO3 ± δ(R = Rare Earth) Solid Solutions

Nd_{1 – x} Ba _x MnO_{3 ±} (0.1 x 0.5) and R_0.7Ba_0.3MnO_{3 ±} (R = La, Pr, Sm, Eu) solid solutions were prepared from nitrate mixtures by solid-state reactions in air and were characterized by x-ray diffraction and thermogravimetry. The oxygen content of the solid solutions was determined by iodometric titration. The materials were found to have a nearly perfect oxygen stoichiometry ( 0). As shown by pH measurements, the solid solutions have a high water resistance (extent of water degradation no larger than 0.1%). The dissociation of the Nd_{1 – x} Ba _x MnO_{3 ±} (0.2 x 0.4) solid solutions was studied as a function of temperature and oxygen partial pressure (–10 log(Po ₂/Pa) 1.4) by a special TG technique.     

Ageing studies of discontinuous copper and silver thin films

The results of experiments carried out on the post-deposition resistance changes in discontinuous films of copper and silver with and without overlayers of SiO and Al₂O₃ are presented. The changes in the sheet resistance of the films with time and pressure were studied for the above combinations. Mobility coalescence is assumed to be responsible for the resistance increase of an uncovered copper film of initial resistance 1.9 M/. On exposure to the atmosphere, it was found that an Ag/SiO combination of initial resistance of 0.1 M/ achieved stability in the sheet resistance much quicker than a Cu/Al₂O₃ combination of initial resistance 20 M/. The fall in resistance of the Cu/Al₂O₃ composite is attributed to the formation of Al₂(OH)₆ due to the interaction of Al₂O₃ with the water vapour in atmosphere. Copper films with and without overlayers of Al₂O₃ show an abrupt increase in the sheet resistance as a function of pressure at a pressure of about 5 × 10^–2 torr with the maximum rate of change of resistance occurring at higher pressure for the higher resistance film. This indicates that the overlayer of Al₂O₃ is very porous in nature. Field effect studies were carried out on an uncovered copper film of initial resistance 10 M/ and the behaviour was found to be ohmic up to a field of 800 V cm^–1.     

Structure and Diamagnetic Properties of (Pb0.6SnyCu0.4 ? y)Sr2(Y1 ? xCax)Cu2Oz

The effect of Sn doping in (Pb_0.6Sn _y Cu_{0.4 – y} )Sr₂(Y_{1 – x} Ca _x )Cu₂O _z with 0 y 0.3 and 0 x 0.7 was investigated. It was established that a nearly pure 1212 phase can be obtained at 0 y 0.1 and 0 x 0.3. The obtained XRD patterns as well as the results of the EDX and ICP-AES analyses showed that Sn substitution is possible in the (Pb,Cu)-1212 phase. Superconductivity was observed at 0.4 x 0.7. The onset of the diamagnetic transitions varied from 10 to 30 K. The influence of the strong Pb deficiency on the superconducting properties of the samples was discussed.     

Ferromagnetic Resonance in Ga1?xMnxAs

We report on ferromagnetic resonance measurements of Ga_1–x Mn _x As thin films with Mn contents 0.022 x 0.051. For x 0.036 and the external magnetic field normal to the thin film, we observe several resonances, which we identify as spin wave resonances. The non-quadratic mode spacing can be consistently explained by a linear gradient in the magnetic properties of the films. From the measurements, the exchange constant A can be deduced for different Mn contents x.     

Y xBayCuzO7− δ solid solutions

Y_xBa_yCu_zO_7– ceramics forming at isobaric conditions were studied by x-ray diffraction analysis, dynamic magnetic measurements and potentiometric titration. It was established that compositions: 0.8 x 1.2 y=2, z=3; x-1, 1.8 y 2.2, z=3; x=1, y=2, 2.7 z 3.4: are in the homogeneity range of 123. It was found that compositions with nonstoichiometric cations rations have minimum T_c.     

Phase transformations of δAl2O3 (Saffil) fibres during their interaction with molten MgLi alloys

The phase transformation of Al₂O₃ occurring in Saffil fibres during their infiltration with molten Mg-8 wt% Li alloy was studied by secondary ion mass spectroscopy, X-ray diffraction and infrared spectroscopy methods. It has been shown, that lithium penetrates very quickly into the whole fibre volume, attaining up to Li/Al 0.25–0.30 ion ratio. The metastable spinel-like compound, (Li), was formed by incorporation of Li⁺ ions into the Al₂O₃ lattice in which the basic spinel structure unit has been assigned by the formula Al₈ [Al(_40–x)/3(_8–2x )/3]Li _x ]O₃₂. During long-term annealing, a further transformation (Li) LiAl₅O₈ proceeded, and LiAlO₂ aluminate was also identified in Saffil fibres with high Li/Al concentration ratio values. In parallel with lithium, magnesium also penetrated the Saffil fibres within an infiltration period; however, the incorporation of magnesium into the spinel lattice has not been observed.     

Non fermi liquid ground states in strongly correlated f-electron materials

Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for three f-electron systems: M_1–xU_xPd₃ (M = Sc, Y), U_1–xTh_xPd₂Al₃, and UCu_5–xPd_x. The emerging systematics of NFL behavior in f-electron systems, based on the present sample of nearly ten f-electron systems, is updated. Many of the f-electron systems exhibit the following temperature dependences of the electrical resistivity p, specific heat C, and magnetic susceptibility for T T₀, where T_o is a characteristic temperature: P(T) 1 –aT/T ₀, where a < 0 or > 0, C(T)/T (-1/T _o) In (T/bT ₀), and (T) 1 –c(T/T_o)^1/2. In several of the f-electron systems, the characteristic temperature T_o can be identified with the Kondo temperature T_k.     

Structural and dielectric properties of solid solutions of sodium niobate in lanthanum and neodymium niobates

Experimental evidence is presented for the formation of continuous series of Ln_{2/3 – x}Na_{3x4/3 – 2x}Nb₂O₆ (Ln = La, Nd) perovskite-like solid solutions. Increasing the Na content of the solid solutions reduces their symmetry from Pmmm to Pmmn and then to Pbcm. The structural and dielectric properties of the solid solutions belonging to the three space groups are studied.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1508–1514.Original Russian Text Copyright © 2004 by Mishchuk, Vyunov, Ovchar, Belous.