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Hafnia (HfO2) is a promising material for emerging chip applications due to its high-κ dielectric behavior, suitability for negative capacitance heterostructures, scalable ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO2 crystals stabilized with yttrium (chemical formula HfO2: xY, where x = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO2 and paves the way for an analysis of mode contributions to high-κ dielectric and ferroelectric properties for chip technologies. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) has emerged as a powerful tool for research in ferroelectric and piezoelectric materials. While the vertical PFM (VPFM) mode is well understood and applied at a quantitative level, the lateral PFM (LPFM) mode is rarely quantified, mainly due to the lack of a practical calibration methodology. Here by PFM imaging on a LiNbO3 180° domain wall, we demonstrate a convenient way to achieve simultaneous VPFM and LPFM calibrations. Using these calibrations, we perform a full quantitative VPFM and LPFM measurement on a (001)-cut PbTiO3 single crystal. The measured effective piezoelectric coefficients def f 33 and def f 35 together naturally provide more information on a material's local tensorial electromechanical properties. The proposed approach can be applied to a wide variety of ferroelectric and piezoelectric systems. [ABSTRACT FROM AUTHOR]

It has been suggested that an awareness of the inclination of systems of charge and spin in the formation of stripe phases may help in the comprehension of the physics of high temperature superconductors. New research investigates a new pattern of charge localization in a two component Bose-Einstein condensate formed from rubidium and sodium atoms.

Resistivity, thermoelectric power, Hall effect, and magnetic susceptibility measurements are reported in the normal state of the high-Tc compounds YBa2Cu3O7-y and GdBa2Cu3O7-y. The results are different from those expected for an uncorrelated metallic band. We suggest that Coulomb interactions are important and that the interaction energy is comparable to or larger than the uncorrelated bandwidth, leading to moderately heavy-fermion-like behavior in the normal state. The Sommerfeld coefficient calculated from the susceptibility indicates that the electron-phonon coupling constant at Tc is not unusually large. © 1987 The American Physical Society.

Magnetic-susceptibility and magnetization measurements on single crystals of the CuO2-planar compound Gd2CuO4 indicate copper moment ordering near 260 K, producing an internal field at the gadolinium site that induces substantial anisotropy in the magnetic response. Dilute substitutions for gadolinium and copper leave the essential physics unaffected. We suggest that copper ordering also occurs in Eu2CuO4 on the basis of substitutional studies but is not detected in other rare-earth-based compounds in this series. Rare-earth size appears to play an important role. © 1989 The American Physical Society.

We have determined the structure of the newly discovered electron-doped superconductor Nd1.85Ce0.15CuO4- at 11 and 300 K using high-resolution neutron-powder-diffraction techniques. Both nonsuperconducting oxygenated and superconducting Zr-gettered (Tc=24 K with shielding and Meissner fractions of 30 and 16% at 5 K, respectively) samples were investigated to study the effect of Zr gettering on the crystal structure and oxygen stoichiometry. We find that the structure remains tetragonal (I4/mmm), with no evidence for Nd/Ce ordering, for both samples at both temperatures. Structure and oxygen stoichiometry of the oxygenated and Zr-gettered samples remain remarkably similar at both temperatures, the only difference being a slight decrease (but greater than three standard deviations) in the thermal parameters of the rare-earth ions along the c axis for the superconducting sample. Thermogravimetric analyses confirm the oxygen stoichiometry determined from the structural refinements. © 1989 The American Physical Society.

A careful study of the metamagnetic transition in single-crystalline La2CuO4 is presented. From magnetic susceptibility measurements the critical exponent () of the weak ferromagnetic state, which terminates at a triple point, has been estimated to be =0.50.02, a value consistent with mean-field theory. Furthermore, the pressure dependence of the critical magnetic field for the transition has been examined from magnetoresistance measurements under hydrostatic pressure. © 1989 The American Physical Society.

Inelastic light scattering studies of La2CuO4, both pure and doped with lead, over the energy range 01 have revealed the presence of high-frequency A1g scattering components, in the spectral region 35006000 cm-1, while also providing the complete line shape for the previously reported spin-pair mode of B1g symmetry. Two main bands, broad and overlapping, are observed in this region with maxima near 3500 and 5200 cm-1. The various spectral features show different resonance behavior. We suggest that a model based upon coupled spin and charge excitations will be required to describe these spectra. © 1989 The American Physical Society.

We have measured the temperature dependence of the resistance for a La2CuO4+ single crystal at pressures from 1 bar to 18 kbar. The effects of pressure on the antiferromagnetic transition temperature TN and the superconducting transition temperature Tc are compared to those of oxygen doping. © 1989 The American Physical Society.

We have measured resistivity ρ components both parallel and perpendicular to the Cu-O planes in single-crystalline La2CuO4. Substantial anisotropy, reaching values as large as 103, is observed in the resistivity. The temperature dependence of ρ, together with Hall effect and thermoelectric power measurements, suggests hopping conduction between localized states at low temperatures, with diffusive transport at higher temperatures. These results are in contradistinction to previous reports. © 1988 The American Physical Society.

High-energy inelastic neutron scattering is used to resolve spin waves in La2CuO4. The corresponding long-wavelength velocity is 0.85±0.03 eV AÌ, well above previous bounds set by thermal neutron scattering. Within experimental error, conventional spin-wave theory gives an excellent description of the magnetic dynamics for momentum and energy transfers below 0.15 AÌ-1 and 0.1 eV, respectively. Doping with Ba changes the magnetic dynamics; the data indicate a combination of spin-wave softening and damping effects. © 1989 The American Physical Society.

The first low-temperature photoemission spectra from well-oxygenated and characterized, cleaved single crystals of the 1:2:3-type superconductors, specifically EuBa2Cu3O7-x, are presented. In contrast with polycrystalline or higher-temperature single-crystalline studies, a distinct and very stable density of states is found at the Fermi edge below 20 K. As the crystal is warmed even to 80 K the emission is rapidly lost from both the upper and lower portions of the Cu-O hybrids. At room temperature there is a loss of intensity at the Fermi edge with an accompanying change in the Ba 4d core-level line shape and the presence of a charging effect indicative of an insulating surface. These results imply that upon warming from 20 K there is very rapid oxygen loss from the cleaved surface with a resulting loss of superconducting behavior. This suggests that future photoemission experiments, especially those investigating detailed band structure, should be performed at low temperatures. © 1988 The American Physical Society.

Our attempts to observe the antiferromagnetic resonance (AFMR) modes in La2CuO4+y in both single crystal and small particle forms have been unsuccessful. An argument based on a magnetic-susceptibility sum rule shows that the resonance previously identified with the AFMR in polycrystalline La2CuO4+y [R. T. Collins, et al., Phys. Rev. B 37, 5817 (1988)] is too strong to be compatible with a magnetic spin-wave mode. No evidence of an AFMR mode is found in our single-crystal La2CuO4+y transmission measurements versus magnetic field. Additional measurements on small particles show that the broad resonant feature observed around 8 cm-1 is produced by an electric-dipole-active superconducting sphere resonance of the La2CuO4+y particles. © 1989 The American Physical Society.

High-pressure (3 kbar) oxygenation of (La, Sm, Sr)2CuO4 compounds having the T* structure leads to bulk superconducting transitions above 30 K and the appearance of a diamagnetic response at temperatures as high as 1/437 K. With increasing oxygenation pressure, the electrical resistivity and thermoelectric power progress from hoppinglike to more nearly metalliclike transport. The similarity in Tc and transport character with those of T-phase La2-xSrxCuO4, despite significant structural differences, further constrains possible mechanisms for superconductivity in the cuprates. © 1989 The American Physical Society.

The anisotropic electrical resistivity and thermoelectric power S have been determined on single crystals of La2CuO4 in which the hole doping has been varied by controlled anneals. An enormous decrease and hysteresis in both and S occur at the Néel temperature TN for small, suggesting strong coupling between magnetic order and transport. Possible origins of these transport anomalies are discussed. © 1989 The American Physical Society.

We have measured the electron-spin-resonance spectrum of Gd3+ ions substituting for Eu ions in Eu2CuO4. The fine structure of the spectrum was partially resolved at room temperature and the individual transitions were completely separated below 100 K. The spectrum is described with a crystal-field effective Hamiltonian of tetragonal symmetry. The values obtained at low temperatures for the corresponding parameters are b20=-486(7)×10-4 cm-1, b40=-32(2)×10-4 cm-1, and |b44|=790(50)×10-4 cm-1. These parameters are only weakly temperature dependent. The measured effective g value is shifted from the free-ion value g=1.992, indicating the existence of antiferromagnetic exchange interactions with the ions of the host. © 1988 The American Physical Society.

Magnetic susceptibility measurements have shown anisotropic Van Vleck paramagnetism in Eu2CuO4 single crystals. This behavior is associated with the singlet ground state (7F0) of Eu3+ ions, and the measured anisotropy is related to a crystal-field splitting of the excited multiplets (7FJ). From the experimental data at low temperatures (T50 K) a crystal-field parameter A20r2=-93(5) cm-1 and a spin-orbit coupling constant =303(15) cm-1 have been estimated. The temperature dependence of the magnetic susceptibility is predicted in terms of the Boltzmann population of the excited multiplets, and a comparison with experimental data up to 350 K is made. The possibility of a magnetic contribution arising from the Cu ions is discussed in connection with some discrepancies observed between the experimental and calculated magnetic susceptibilities. © 1989 The American Physical Society.

We have performed angle-integrated photoemission measurements at 20 K on well-oxygenated (Tc=92 K) single crystals of YBa2Cu3O6.9 cleaved n situ, and find a relatively large, resolution-limited Fermi edge which shows large amplitude variations with photon energy, indicative of band-structure final-state effects. Some dispersion is seen even in our angle-integrated measurements. Our best estimate of N(EF) per Cu atom is that it is about 20% that of Cu metal with about a 20-80 mix of Cu 3d and O 2p orbitals. Dispersive and final-state effects are seen throughout the valence bands. The line shapes of the spectra as a function of photon energy are very well reproduced by band-structure predictions, indicating a correct mix of 2p and 3d orbitals in the calculations, while the energy positions of the peak agree with calculated bands to within 0.5 eV. We conclude that a Fermi-liquid approach to conductivity is appropriate. © 1989 The American Physical Society.

Magnetic susceptibility and isothermal magnetization measurements on single crystals of Y2Cu2O5 show evidence for two field-induced phase transitions that develop out of an antiferromagnetic ground state. © 1988 The American Physical Society.

We have measured the electrical resistivity, thermoelectric power, magnetic susceptibility, Hall coefficient and upper critical field near Tc in EuBa2Cu3Ox, where 6.09

The magnetic field dependence of the three dimensional magnetic ordering transition has been examined in single crystalline La2CuO4-δ by magnetization and magnetoresistance measurements. We establish a phase diagram in the magnetic field-temperature plane and point out similarities to metamagnetic transitions observed in other magnetic systems. © 1988.

We review the crystal chemical, electronic, magnetic and superconducting properties of La2CuO4 and related planar-cuprate materials, with emphasis on single-crystal results. Although magnetism due to divalent copper ions clearly is evident in nonsuperconducting crystals, experiments do not reveal any direct relationship between localized copper spins and high temperature superconductivity. We also indicate areas where important information is lacking for our understanding of these materials. © 1989.

Valence band photoemission spectra of single crystals of EuBa2Cu3O6.7, cleaved and measured at T=20 K, are presented. A stable Fermi edge is observed, whose amplitude is ≈10% of the maximum valence band intensity. This suggests metallic behavior. Except for 1 eV shift toward higher binding energy, the results compare favorably with previous band calculations, and hint at a re-examination of theories based purely on a localized electronic structure. There is evidence for both Cu-3d and O-2p occupation at EF, as predicted by band calculations. © 1988.

We report electrical resistance and magnetoresistance measurements on EuBa2(Cu1-yZny)3Ox under pressures to 17 kbar. With Zn substitution, Tc is depressed rapidly (∼19 K/ at.% Zn) and there are qualitative changes in the temperature and field response of the resistance. Pressure drives the Zn-substituted samples toward undoped EuBa2Cu3Ox behavior. Analysis of the temperature dependent resistance for y=0.05 and P=0, together with Hall effect and thermopower data, suggests that the suppression of superconductivity may arise from weak three-dimensional localization promoted by Coulomb interactions. © 1987.

A systematic study of the phase stability of La(Pr)2-x-yRxSr(Ba, Ca)yCuO4 (R = rare earth) compounds reveals a broad composition range for T*-phase formation. Several members of this series of compounds show bulk superconducting transition temperatures up to Tc ∼ 20 K. These superconducting cuprates raise further questions about the relationship between structural stability and high temperature superconductivity in oxides. © 1989 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division).

We report the discovery of a new phase diagram in the magnetic field-temperature plane for single crystals of La2CuO4 that show no sign of antiferromagnetic order. The phase boundary is defined by magneto-resistance and susceptibility measurements. We discuss several possibilities that may lead to the phase diagram observed. © 1988.

EPR, microwave absorption, and dc magnetization measurements were made on single crystals of the form R2CuO4, which are the host compounds for the newly discovered series of electron cuprate superconductors. These measurements reveal two characteristic transition temperatures associated with a novel complex magnetic behavior, including weak ferromagnetism, two sharp peaks in the low field DC magnetization, an unusual anisotropy in the EPR resonance field for R = Gd, and two additional anisotropic microwave absorption modes. The higher characteristic transition temperature, at ≈270K, is attributed to AF ordering of the Cu moments, and the lower, at ≤20K, to a spontaneous canted spin reorientation. An understanding of this magnetic behavior is important in order to ascertain its relationship to possible mechanisms of high temperature superconductivity. © 1989.

The T{star, open}-phase is a mixed rare earth oxide phase forming at the composition R2CuO4. Its crystal structure is intermediate between the La2CuO4 and Nd2CuO4 structures. Sr-doped samples have Tc onsets as high as 37 K. We discuss the systematics of Tc of T{star, open}-phases as a function of Sr doping, rare earth mixture and oxygenation. Structural and transport data will also be presented. © 1989.

We report measurements of the superconducting and magnetic behavior of GdBa2Cu3Ox. Superconductivity occurs below Tc = 95 and 93 K, respectively, for these compounds with large Meissner effects observed. The Gd-based compound has an upper critical field slope -dHc2 dT greater than 1.2 T/K. Both compounds exhibit Curie-Weiss behavior above Tc with free-ion effective moments and small, negative temperature intercepts. In addition, the Gd-based compound orders antiferromagnetically below 2.24 K with an entropy consistent with the ordering of seven unpaired spins. © 1987.

Neutron and X-ray diffraction have been used to study the magnetic and structural properties of single crystal Nd2CuO4. Long range magnetic order of the Cu moments develops at TN=245 K, with a noncollinear antiferromagnetic arrangement of spins. Additional abrupt transitions are observed at 75 K and 30 K, in which a spin reorientation takes place. Bragg peaks associated with the crystal structure are found at the same positions as the magnetic Bragg peaks, and indicate that a distortion of the basic tetragonal structure has occurred above 300 K. © 1989.

We report the superconductivity of R-Ba-Cu-O compounds for rare earths R = Sm through Ho. The Nd and Tm compounds were not observed to be superconducting. The Tc onsets for the Eu and Gd compounds are comparable to that observed for Y-Ba-Cu-O. An approximate value for the upper critical field slope of the Gd compound is given. © 1987.

Specific heat and magnetic susceptibility measurements on single crystals of RE2CuO4 (RE=Pr, Nd, and Sm) indicate antiferromagnetic order at TN≲1.5 K and 5.95 K for RE = Nd and Sm, respectively. The susceptibility of all RE2CuO4 compounds is highly anisotropic and suggests the presence of crystal field effects. © 1989.