Dielectric and piezoelectric properties of (1 ? 2x)BiScO3 · xPbTiO3 · xPbMg1/3Nb2/3O3 (0.30 ≤ x ≤0.46) solid solutions

We have synthesized ceramic samples of (1 − 2x)BiScO₃ · xPbTiO₃ · xPbMg_1/3Nb_2/3O₃ perovskite solid solutions with 0.30 ≤ x ≤ 0.46 and studied their structural, dielectric, and piezoelectric properties. At x = 0.40, the system has a morphotropic phase boundary between tetragonal (x > 0.40) and rhombohedral (x < 0.40) solid solutions. The dielectric permittivity and loss tangent of the solid solutions have been measured at temperatures from 100 to 800 K and frequencies from 0.1 to 200 kHz. The maximum in the permittivity of the solid solutions lies in the range 390–440 K. With increasing BiScO₃ content, features characteristic of fer-roelectric relaxors emerge and become more pronounced. Near the morphotropic phase boundary, the piezoelectric charge coefficients d ₃₃ and d ₃₁ of the solid solutions reach 410 and 150 pC/N, respectively, and their radial-mode mechanical Q drops to 22, which makes these materials potential candidates for a number of applications.     

On the phase relations in the VxMo1−xO2 system (0 ≤ x ≤ 0.55)

The pseudo-binary system V_xMo_1?xO₂ (0 ≤ x ≤ 0.55) has been studied by X-ray examination of samples quenched after prolonged heat-treatment at temperatures between 400°C and 1190°C. The phase diagram is complicated, with several rutile-related phases. The approach to equilibrium is sluggish in some areas.     

Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

Ferroelectric, dielectric and piezoelectric properties of Pb1?xCex(Zr0.60Ti0.40)O3, 0?≤?x?≤?0.08

The ferroelectric, dielectric and piezoelectric properties of compositions Pb_1−x Ce _x (Zr_0.60Ti_0.40)O₃, (x = 0.0, 0.01, 0.02, 0.04, 0.06 and 0.08) are studied. The above compositions are prepared from their constituent oxides, calcined at 900 °C for 4 h and various phases present are characterized by X-ray diffraction (XRD) technique. The above powders are uniaxially pressed into circular compacts, sintered at 1,250 °C for 2 h, electroded, poled at 2 kV/mm D.C. voltage and their electrical properties are measured. The XRD analysis shows the presence of rhombohedral phase up to 2 mol% ceria while tetragonal phase found at higher concentrations. It is observed that the ferroelectric, dielectric and piezoelectric properties increase with the addition of ceria with a maximum at 2 mol% and then decreases. The higher piezo properties associated with low ceria concentration are attributed to rhombohedral phase.     

Synthesis and structural characterization of (Bi2O3)1?x (Y2O3)x and (Bi2O3)1?x (Gd2O3)x solid solutions

Solid solution series, (Bi₂O₃)_1−x (Y₂O₃)_x and (Bi₂O₃)_1−x (Gd₂O₃)_x, forx = 0.10, 0.20, 0.30 and 0.40 were synthesized by standard ceramic technique. The structural phase characterization was carried out using X-ray powder diffraction technique. It was found that the solid solution containing 20–40 mole% of Y₂O₃ had face-centred cubic structure. All samples of the solid solution series, (Bi₂O₃)_1−x (Gd₂O₃)_x, had rhombohedral single phase in the concentration range 0.10 ≤x ≤ 0.40. Lattice parameters offcc phase of Y₂O₃ doped samples were calculated from the X-ray diffraction data. The lattice constant ‘a’ gradually decreases with increasing content of dopant concentration (x) for the Y₂O₃ doped system and obeys Vegard’s rule. The unit cell parameters for the (Bi₂O₃)_1−x (Gd₂O₃)_x doped samples showing rhombohedral phase were obtained on hexagonal setting.     

Structural and dielectric properties of the phase Pb1−2xKxM3+xNb2O6, M = La or Bi

The Pb_1?2xK_xM³⁺_xNb₂O₆, M = La or Bi, solid solutions have been prepared by solid state reaction and their structural and ferroelectric properties have been established. Complete crystalline solid solubility exists in both systems; in addition, three structurally related phases, namely, the ferroelectric orthorhombic and tetragonal tungsten bronze phases and the paraelectric tetragonal K.₅La.₅Nb₂O₆ type phase, have been identified at room temperature. The composition ranges for three phases are 0.0 ≤ x ≤ 0.47, 0.48 ≤ x ≤ 0.85, 0.86 ≤ x ≤ 1.0, respectively. The ferroelectric phase transition temperature, T_c, decreases with increasing concentration of K⁺ and La³⁺ or Bi³⁺ in the orthorhombic tungsten bronze phase. A few compositions from each system exhibit excellent dielectric and piezoelectric characteristics, indicating that they could be future materials for piezoelectric and high frequency dielectric studies.     

On the proton conductor (H3O)Zr2(PO4)3

The compound HZr₂(PO₄)₃ was converted to (H₃O)Zr₂(PO₄)₃ by refluxing in water for 12 or more hours. The water is lost above 150°C to regenerate the original triphosphate. The hydronium ion phase is rhombohedral with hexagonal axes of a = 8.760(1) and $\text{c}\text{= 23.774(4)}\text{A}\text{?}$. Proton conduction in these compounds was investigated by an ac impedance method over the frequency range 5Hz – 10MHz. The activation energy for (H₃O)Zr₂(PO₄)₃ in the temperature range of 25 to 150°C was 0.56eV while the corresponding value for HZr₂(PO₄)₃ (125 – 300°C) was 0.44eV.     

Preparation of pyrochlores. A1−xHxTaO3·nH2O (A=Na,K)

Pyrochlores of A_1?xH_xTaO₃·nH₂O (A=Na,K) were prepared under the hydrothermal conditions. The values of x for these compounds were increased from 0.3 to 0.5 for A=Na and from 0.2 to 0.5 for A=K by treatment with the distilled water. The compounds with x<0.5 were decomposed to a mixture of NaTaO₃ and Na₂Ta₄O₁₁ for A=Na, or to a mixture of KTaO₃ and a tetragonal tungsten bronze phase, and those with x=0.5 to a single phase of A₂Ta₄O₁₁ at elevated temperatures. Below the decomposition temperatures, defect pyrochlores with oxygen vacancies, $\text{A}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{TaO}{}_{\mathrm{<mtext>3?</mtext><mtext>x</mtext><mtext>2</mtext>}}$, were produced. They were hygroscopic, and in the case of A=K and x=0.5 the original phase was recovered by leaving in air for several hours.     

Study of carbon-substituted EuB6

Carbon-substituted europium hexaborides EuB_6-xC_x have been prepared by borothermal reduction. The homogeneity range is 0 ≤ x ≤ 0.21. The lattice parameter decreases progressively from 4.1855 Å to 4.1703 Å with rising x. The paramagnetic Curie temperature diminishes from 15 to ? 6.5 K. Electrical properties have been studied for x = 0 and x = 0.05 on single crystals prepared by an Al-flux technique. Between 30 and 300 K both single crystals have metallic behavior and their resistivity at 300 K is of the order of 10^?4 Ω .cm. However each single crystal shows a rather different temperature-dependence of resistivity at low temperature.     

Depolarization temperature and piezoelectric properties of Na1/2Bi1/2TiO3-Na1/2Bi1/2(Zn1/3Nb2/3)O3 ceramics by two-stage calcination method

A new group of NBT-based lead-free piezoelectric ceramics, Na_1/2Bi_1/2TiO₃-Na_1/2Bi_1/2(Zn_1/3Nb_2/3)O₃, was synthesized using the two-stage calcination method and depolarization temperatures and piezoelectric properties were also investigated. The XRD analysis showed that the ceramics system had a morphotropic phase boundary (MPB) between the rhombohedral and the tetragonal structure. The highest piezoelectric properties of d ₃₃ = 97 pC/N and k _t = 0·46 were obtained near MPB compositions. Furthermore, the depolarization temperatures near MPB compositions were slightly decreased and the lowest T _d was maintained at 210°C.     

Preparation of sodium zirconium phosphates of the type Na1+4xZr2−x (PO4)3

Sodium zirconium phosphates of the type Na_1+4x Zr_2?x (PO₄)₃ were prepared from mixtures of Na₃PO₄-ZrO₂-ZrP₂O₇ in sealed platinum tubes at temperatures of 900 – 1200°C. Stoichiometric NaZr₂ (PO₄)₃ (x = 0) was found not to exist. Instead, a solid solution in the range x = 0.02 ? 0.06 was found, with a slight difference in unit cell dimensions obtained. A second solid solution region was found with x = 0.88 – 0.93. At still higher values of x, a stoichiometric phase with hexagonal unit cell dimensions of $\text{a}\text{= 9.152(1)}\text{A}\text{?}$ and $\text{c}\text{= 21.844(1)}\text{A}\text{?}$ was obtained. Finally a phase of composition Na₇Zr_0.5 (PO₄)₃ was synthesized at the highest values of x. Attempts to prepare Na_5+x ZrSi_x-P_3?xO₁₂ always yielded NASICON and Na₇Zr_0.5 (PO₄)₃.     

Solid solution single crystals: (1−x)HoF3·xErF3

The orthorhombic phase of the single crystal, (1?x)HoF₃·xErF₃ at 0 ≤ x ≤ 1, was grown directly at the melting point. Type 1 solid-solution behavior was observed. The solidus-liquidus concentration gap was fairly narrow. The results indicate the solution to be close to ideal.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

Crystal structure of new superconducting materials LaIrSi3 and LaRhSi3. Structural relation between LaRh2Si2, La2Rh3Si5 and LaRhSi3

New superconducting ternary silicides LaRhSi₃ and LaIrSi₃ have been prepared by arc melting from the elements and annealing for ten days at 900°C. A single crystal study shows these materials to be of tetragonal symmetry and isostructural with BaPtSn₃. Their superconducting transition temperature which depends strongly on stoichiometry and thermal treatment occurs between 1.9 K and 2.7 K. The structures have been compared to those of the superconducting compounds LaRh₂Si₂ and La₂Rh₃Si₅. The occurence of superconductivity in these materials seems to be related to the presence of similar coordination polyhedra for Rh or Ir and Si atoms.     

Bronzoid phases in the pseudo-binary system AxNbxW1−xO3 with A = K and Cs

The systems A_xNb_xW_1?xO₃, A = K, Cs, have been studied at 1200°C for compositions x < 0.5. Phases with intergrowth tungsten bronze (ITB) structure form for x ～ 0.08 – 0.12 and with hexagonal tungsten bronze (HTB) structure for x ～ 0.20 (with a small homogeneity range). The potassium system contains a tetragonal tungsten bronze (TTB)-type phase at x ～ 0.45 – 0.60 and cesium forms a pyrochlore phase at x～0.35 – 0.40. The alkali contents of the HTB and pyrochlore phases are considerably lower than those of phases prepared at 900°C. The tunnel occupancy is approximately the same, ～ 60 %, in the ITB, HTB and pyrochlore phases prepared at 1200°C. Two types of superstructures have been observed in the HTB-type crystals.     

New phases in the systems EuF2:YF3 and EuF2:GdF3

Isothermal pseudo-binary phase studies of the systems EuF₂:YF₃ and EuF₂:GdF₃ have been completed at 1100°C. Three single phase regions corresponding to (1) EuF₃(ss); (a) hexagonal tysonite and (3) orthorhombic LnF₃(ss), Ln = Y, Gd, have been found. The single phase regions for both of these systems are similar and exist at 0–39, 73–82 and 91–100 mole % YF₃; 0–41, 70–77 and 85–100 mole % GdF₃.     

Conductivite anionique des phases du systeme PbF2 | SbF3

A solid solution Pb_1?xSb_xF_2+x (0 < x ≤ 0.40) of fluorite type and a definite Pb₂Sb₃F₁₃ phase have been obtained at 250°C in the PbF₂|SbF₃ system. The study of the variation of the ionic conduction shows that Pb_0.75Sb_0.25F_2.25 is a good ionic conductor.     

Preparation and some properties of rare earth iron borates,RFe3 (BO3)4

A new series of rare earth iron borates having the general formula RFe₃(BO₃)₄ (R=Y, Nd, Sm, Gd, Dy or Ho) was synthesized. The compounds were isostructural with huntite, CaMg₃(CO₃)₄, like other rare earth double borates, RM₃(BO₃)₄, M=A1 or Ga. Single crystals of Y and Gd compounds were grown by the flux method. Thermomagnetic measurements indicated that all the compounds are paramagnetic and have no spontaneous magnetization between 78°K and 730°K.     

Morphotropic phase boundary in the system Pb(ZrxTi1−x)O3

The room temperature phase boundary dividing the rhombohedral and tetragonal in the solid solution system lead zirconate titanate Pb(Zr_xTi_1?x)O₃ is examined carefully using an ultrahomogeneous synthesis technique. There is no evidence for a broad transition region of co-existing phases as understood earlier but a sharp boundary located at x = 0.510 ± 0.002.     

Temperature dependence of critical stress and phase diagram of ferroelastic Pb3 (PO4)2 Pb3 (VO4)2

The temperature dependence of the critical stress in ferroelastic Pb₃ (PO₄)₂ reveals a Curie-Weiß law ($\text{ß =}\text{1}\text{2}$) up to 145°C. Between 160°C and the transition point at 180°C a crossover to a $\text{ß =}\text{1}\text{3}$ regime was found. For mixed crystals Pb₃ (PO₄)₂ ? Pb₃ (VO₄)₂ a phase diagram is suggested from optical, dielectric and Raman spectroscopical experiments.