Showing papers on "Tetragonal crystal system published in 1978"
903 citations
TL;DR: In this article, a stress-induced phase transformation in the metastable tetragonal phase of polycrystalline zirconia was shown to increase the strength and grain size.
Abstract: Polycrystalline zirconia containing a high content of metastable tetragonal phase shows high strength (∼ 700 MPa), high fracture toughness (Kc = 6 to 9 MN m−3/2) and small grain size (<0.3jμm). The strength and grain size remain nearly constant over a wide range of tetragonal phase content (100 to 30%). At a low concentration of tetragonal phase <30%, there is a rapid decrease in strength accompanied by a rapid increase in grain size. These results are explained by means of a stress-induced phase transformation in the metastable tetragonal phase.
438 citations
166 citations
TL;DR: In this article, the growth morphology of the tetragonal phase in partially stabilized zirconia was examined using electron microscopy and electron and X-ray diffraction, and it was found that the TPT is retained at room temperature provided coherency with the cubic matrix is retained.
Abstract: The zirconia-rich, metastable tetragonal phase in partially stabilized zirconia—magnesia, zirconia—calcia and zirconia—yttria is examined using electron microscopy and electron and X-ray diffraction. The tetragonal phase precipitate distribution is that normally associated with homogeneously nucleated coherent precipitation. An attempt is made to explain the growth morphology of the tetragonal phase in terms of the cubic—tetragonal lattice parameter mismatch. It is found that the tetragonal phase is retained at room temperature provided coherency with the cubic matrix is retained. Once coherency is lost, due to growth strains or mechanical influences, the precipitate reverts to the room temperature stable monoclinic form.
138 citations
TL;DR: Stoichiometric CaFeO 3 was prepared and was characterized by crystallographic, magnetic and electrical measurements as mentioned in this paper, which indicated a phase transition from the metallic-paramagnetic (the high-temperature phase) to the semiconductive-antiferromagnetic phase.
135 citations
127 citations
TL;DR: The crystal phases of non-ohmic ZnO ceramics have been investigated by classifying and clarifying them as a function of the amounts of the additives and sintering temperature, and synthesizing their single phases as mentioned in this paper.
Abstract: The crystal phases of nonohmic ZnO ceramics, having Bi2O3, Sb2O3, Co2O3, MnO2 and Cr2O3 as additives, have been investigated by classifying and clarifying them as a function of the amounts of the additives and sintering temperature, and synthesizing their single phases. These ceramics consist of ZnO phase dissolving Co and Mn components, spinel phase of Zn7Sb2O12 dissolving Co, Mn and Cr components, and Bi-rich phases (B, C, D or B'). The B-phase is a δ-Bi2O3 type phase (a=5.59 A) having a fundamental composition of 12Bi2O3Cr2O3. The C-phase is a tetragonal phase (a=7.76 A, c=5.75 A) having a fundamental composition of 14Bi2O3Cr2O3. The D-phase is a β-Bi2O3 type tetragonal phase (a=10.93 A, c=5.62 A) dissolving a large amount of Zn component and a small amount of Sb component. The B'-phase is also a δ-Bi2O3 type phase (a=5.48 A) formed in the system Bi2O3–ZnO–Sb2O3. A solid solution between B and B'-is formed. The nonohmic property of ZnO ceramics is improved with the changes of phases, B→C→D or D+B', by raising the sintering temperature. The extinction of the nonohmic property caused by the change in the amounts of additives and sintering temperature corresponds to that of ZnO or Bi-rich phases in the ceramics.
125 citations
TL;DR: In this paper, the structure and growth characteristics of crystals growing in the amorphous alloys Fe50Ni30B20 and Fe8oB20 were studied by transmission electron microscopy and X-ray diffraction.
Abstract: The structure and growth characteristics of crystals growing in the amorphous alloys Fe50Ni30B20 and Fe8oB20 were studied by transmission electron microscopy and X-ray diffraction. The alloys, in the form of ribbon, were annealed for 2 h at 380° to initiate crystallization. The Fe3B crystals in both alloys have characteristic cylindrical shapes, and their structure is b.c. tetragonal witha = 8.63a andc = 4.29a. Growth occurs by formation of columnar regions which grow outward from the center of the crystal. Twinning on {211} planes of the Fe3B divides the crystals into gradrants. There is a small amount of alpha-iron incorporated in the crystal which has a preferred orientation relationship with the Fe3B. From these results and the results of earlier work, it is seen that the shape and structure of the crystals depend upon the metalloids present in the alloy.
99 citations
TL;DR: In this article, a detailed analysis of X-ray intensities yields all ion locations and interatomic distances in the body centered tetragonal structure (space group I4/MMM).
98 citations
TL;DR: In this article, three allotropic varieties of PbSnF4 -α, β and γ - have been detected by DTA and X-ray diffraction, and the α ai β and β ai γ transitions are reversible and occur at 80 and 355°C respectively.
80 citations
TL;DR: The crystal structure of isotactic poly(4-methyl-1-pentene) was determined by x-ray analysis as discussed by the authors, and the unit cell is tetragonal, P4b2, with α = 18.70 A and c (fiber axis) = 13.68 A; it contains four molecular chains each consisting of seven monomeric units in the fiber period.
Abstract: The crystal structure of isotactic poly(4-methyl-1-pentene) was determined by x-ray analysis. The unit cell is tetragonal, P4b2, with α = 18.70 A and c (fiber axis) = 13.68 A; it contains four molecular chains each consisting of seven monomeric units in the fiber period. The molecular conformation is essentially a (7/2) helix, but deviates slightly from the uniform (7/2) helix. The unusual low density is discussed from the structural point of view.
TL;DR: The boundaries between the normal paramagnetic, superconducting, and normal magnetically ordered phases in the tetragonal pseudo-ternary rare earth system (Er1−xHox)Rh4B4 have been established by means of ac susceptibility measurements to temperatures as low as 0.07 K as discussed by the authors.
TL;DR: In this article, the diffractometer traces were analyzed by a mathematical peak separation procedure which assumed a combined Cauchy and Gaussian shape for the peaks, and the results confirmed that the quenched form contains about 60% of amorphous polypropylene.
Abstract: X-ray diffraction has been used to further investigate the quenched form of polypropylene. The diffractometer traces were analyzed by a mathematical peak separation procedure which assumed a combined Cauchy and Gaussian shape for the peaks. The results confirmed that the quenched form contains about 60% of amorphous polypropylene. In the remainder, the x-ray diffraction peak positions indicate that the chain helices are arranged in a square array and a cubic or tetragonal symmetry is proposed for this phase. The shape of the x-ray diffractometer peaks indicates a degree of strain in the structure. Crystallite sizes, determined from peak breadths, have been estimated as approximately 30 A.
TL;DR: In this paper, an intrinsic, polarized u.v.-absorption of crystalline tetragonal GeO 2 is presented for ∝ in the range 5-10 3 cm -1 at room temperature and below.
TL;DR: The single-crystal elastic constants of tetragonal Al2Cu have been measured over the temperature range 4.2-300 K by the pulse-echo-overlap technique as mentioned in this paper.
Abstract: The single‐crystal elastic constants of tetragonal Al2Cu have been measured over the temperature range 4.2–300 K by the pulse‐echo‐overlap technique. The directly measured constants show a normal monotonic decrease in magnitude with increasing temperature but with C44 showing the least change. The anisotropy ratios C33/C11, C12/C13, and C44/C66 show only small percentage changes between 4.2 and 300 K, but 2C44/(C11−C12) changes by nearly a factor of 2. Comparison of data for Zr2Ni with that for Al2Cu indicates some importance of atomic size effects. A Debye temperature of 402 K was evaluated from the elastic constants at 4.2 K.
TL;DR: The existence of ternary chalcogenides of general composition TlT2X2 (T=Fe,Co,Ni,X=S;T =Fe, Co, Ni,Cu, X=Se) crystallizing in the ThCr2Si2-structure type has been established as mentioned in this paper.
Abstract: The existence of ternary chalcogenides of general composition TlT2X2 (T=Fe,Co,Ni,X=S;T=Fe,Co,Ni,Cu,X=Se) crystallizing in the ThCr2Si2-structure type has been established. The crystal structure of TlCo2S2 was refined from single crystal diffractometer data. The dimensions of the tetragonal unit cells are: TlFe2S2;a=3.755 (1),c=13.35 (1) A; TlCo2S2:a= =3.7410 (5),c=12.956(5) A; TlNi2S2:a=3.792 (1),c=12.77 (1) A; TlFe2Se2:a=3.890 (1),c=14.00(1) A; TlCo2Se2:a=3.847 (1),c=13.54 (1) A; TlNi2Se2:a=3.866 (1),c=13.41 (1) A; TlCu2Se2:a=3.852 (1),c=14.01 (1) A. These phases are the first chalcogenides found to crystallize in the ThCr2Si2-structure type. Unlike the already known representatives of this structure type they show a pronounced partial ionic character. Interatomic distances as well as the relations to the alkali thiometallates of Co and Mn are discussed.
TL;DR: In this paper, the structural and dielectric properties of 0.1Pb0.9K0.95-xPbZrO3-(0. 9-x)PbTio3 solid solutions in the region of morphotropic phase boundary between tetragonal and rhombohedral structures were studied.
Abstract: The structural and dielectric properties have been studied on 0.1Pb0.9K0.1(Zn1/3Nb2/3)O2.95–xPbZrO3–(0.9-x)PbTio3 solid solutions in the region of morphotropic phase boundary between tetragonal and rhombohedral structures. In the X-ray analysis, the{200} reflections which were mainly selected to investigate are split into three lines, in which two are due to the tetragonal structure and central one is due to the rhombohedral structure in the miscibility gap between x=0.43~0.55. The phase boundary between two structures is not a line but a region, where the lattice parameters of each phase remain constant. In the dielectric study, the appearance of two phases is also investigated, being based on the "mixing rule" from the volume fractions and the dielectric constants of two phases. The Curie temperature of each phase does not change in the coexistence region of two phases.
TL;DR: In this paper, the dispersion of the refractive index of tetragonal and ortorhombic bismuth trioxide thin films has been investigated using a single-oscillator model.
Abstract: Transmission spectra of bismuth trioxide thin films, of tetragonal and ortorhombic structures, are studied. Experimental data on the wavelength dependence of the refractive index are presented. The dispersion of the refractive index follows a single-oscillator model. Optical energy gap of tetragonal phase is smaller than that of orthorhombic phase; at 300 K these are 2.6 eV and 2.85 eV and at 77K are 2.8 and 3.1 eV, respectively.
TL;DR: In this article, the cubic net of three-connected silicon atoms (SrSi2 type of structure) can be transformed into the tetragonal one by a high-pressure high-temperature treatment.
TL;DR: In this paper, the crystal and molecular structure of Hg/sub 3/AsF/sub 6/ has been investigated by single-crystal neutron diffraction, and it was shown that the Hg chains are not strictly one-dimensional.
Abstract: The crystal and molecular structure of Hg/sub 3/AsF/sub 6/ has been investigated by single-crystal neutron diffraction. This metallic compound crystallizes in the body-centered tetragonal space group I4/sub 1//amd with cell dimensions of a = 7.549 (5) A and c = 12.390 (9) A. The crystal structure consists of two orthogonal and nonintersecting linear chains of Hg/sup 0.33+/ cations passing through a lattice of octahedral AsF/sub 6//sup -/ anions. The intrachain Hg--Hg distance of 2.64 (2) A is derived from planes of diffuse scattering normal to a* and b*. Since the a and b axis lattice constants are not simple multiples of the Hg--Hg intrachain distance, the mercury chains are incommensurate with the tetragonal lattice; hence we have the apparent formula Hg/sub 2/./sub 86/AsF/sub 6/. These results are in essential agreement with a previously reported x-ray diffraction study. However, from the neutron diffraction data, we have established that the Hg chains are not strictly one-dimensional. The maximum room-temperature deviation from the chain axis is 0.07 (1) A with neighboring chains distorted away from each other. The closest interchain Hg--Hg contact is 3.24 (2) A. Furthermore, analytical data consistently indicate a stoichiometric empirical formula of Hg/sub 3/AsF/sub 6/. These results together withmore » precise density measurements imply that the incommensurate structure is stabilized by anion vacancies, such that there are four formula weights of Hg/sub 2/./sub 86/(AsF/sub 6/)/sub 0/./sub 953/ per unit cell. 4 tables, 2 figures.« less
TL;DR: In this article, the spontaneous birefringence perpendicular to the polar axis of the orthorhombic low temperature phase has been measured versus temperature and silicon contents: the temperature of the phase transition of species 4mmFmm2 is of second order and decreases from 1103 K at 0 at %Si to about 400 K at 40 at % Si.
Abstract: Complete solid solubility is found in the pseudobinary system Ba2TiGe2O8-Ba2TiSi2O8 by studies on ceramics and single crystals (Czochralski technique). The spontaneous birefringence perpendicular to the polar axis of the orthorhombic low temperature phase has been measured versus temperature and silicon contents: the temperature of the phase transition of species 4mmFmm2 is of second order and decreases from 1103 K at 0 at % Si to about 400 K at 40 at % Si. The pyroelectric coefficient in the orthorhombic mm2 and the tetragonal 4 mm phase is of the order of 10−6 C m−2 K−1 in the entire system and has a positive temperature coefficient for all compositions studied except for Ba2TiGe2O8, in which the pyroelectric coefficient changes sign at about 308 K. The spacegroup of the orthorhombic phase is proposed to be C
2v
11
-Cmm2.
TL;DR: In this article, experimental data on the superconducting temperature, and low temperature specific heat, together with X-ray and neutron investigations are reported for two sets of Nb x Sn 1− x, samples with the A15 type structure.
TL;DR: In this article, the tetragonal tungsten bronze-type (K6Ta10.8O30) was solved using conventional methods; of 539 unique reflections measured by counter-methods, 435 that obeyed the condition I ⩾ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.038 (wR = 0.036).
TL;DR: In this article, S-state ions incorporated into PbFCl-type tetragonal single crystals were determined and correlated with structural and physico-chemical properties of the studied compounds.
Abstract: Experimental results are reported on S-state ions incorporated into PbFCl-type tetragonal single crystals. The spin Hamiltonian parameters of these ions are determined and correlated with structural and physico-chemical properties of the studied compounds. The experimental b20 spin Hamiltonian parameters vary linearly with the lattice constant a of the host unit cell. Further, the dependence of the spin Hamiltonian parameters on temperature has been investigated and parametrised. The results of a Raman investigation of the hosts are presented.
TL;DR: In this paper, the lattice parameters of solid CD4 at saturated vapor pressure are reported for temperatures from 4.4 to 60 K. The x-ray results show two first order phase transitions near 26.9 and 22.0 K.
Abstract: Precise measurements of the lattice parameters of solid CD4 at saturated vapor pressure are reported for temperatures from 4.4 to 60 K. The x‐ray results show two first order phase transitions near 26.9 and 22.0 K. For the two cubic phases, the lattice parameter a has been measured to an accuracy of 15 ppm, while for the low temperature tetragonal phase, the parameters c and a have been obtained to roughly 150 ppm. The thermal expansion for all three phases has been calculated from the data. Several interesting properties of the phase transitions are described.
TL;DR: In this paper, an ordered structure in the composition range VN0.74-VN 0.84 of the cubic mononitride phase was found by means of electron diffraction/microscopy.
Abstract: An ordered structure is found in the composition range VN0.74–VN0.84 of the cubic mononitride phase by means of electron diffraction/microscopy. The lattice constant of this structure is twice as large as that of the original NaCl type cell. At the composition VN0.81, or V32N26, six nitrogen atoms are missing from the unit cell. The vacancy arrangement has tetragonal symmetry, and the superstructure belongs to the space group P42/nmc. Disordering of this structure occurs at about 520 °C. The transition entropy determined from heat-capacity measurements agrees well with a calculation based on the crystal structure proposed here. A tentative phase diagram for the composition range VN0.6–VN1.0 is presented.
TL;DR: In this paper, a simple cubic array of tetragonally deformed octahedral complexes is modeled as the Potts model and the phase diagram, the stability of the various phases, the type of transitions, and the temperature dependence of the order parameter are studied in mean-field approximation.
Abstract: Orientational ordering of spontaneously distorted building blocks of a crystal is a mechanism for order-disorder structural phase transitions. We study as a model substance the case of a simple cubic array of tetragonally deformed octahedral complexes. The three equivalent tetragonal deformations along the cube axes are taken as the three states of the Potts model. We investigate the various structures which can appear depending on the type of interaction between the complexes. The phase diagram, the stability of the various phases, the type of transitions, and the temperature dependence of the order parameter are studied in mean-field approximation. We further show that piezodistortive coupling to the elastic strain may stabilize different low-temperature structures, and that it gives rise to a renormalization of elastic constants and to acoustic anomalies.