Crystals

156 KiB

Open AccessArticle

Retrieval of Effective Parameters of Subwavelength Periodic Photonic Structures

by Alexey A. Orlov, Elizaveta A. Yankovskaya, Sergei V. Zhukovsky, Viktoriia E. Babicheva, Ivan V. Iorsh and Pavel A. Belov

Crystals 2014, 4(3), 417-426; https://doi.org/10.3390/cryst4030417 - 17 Sep 2014

Cited by 9 | Viewed by 5099

Abstract

We revisit the standard Nicolson–Ross–Weir method of effective permittivity and permeability restoration of photonic structures for the case of subwavelength metal-dielectric multilayers. We show that the direct application of the standard method yields a false zero-epsilon point and an associated spurious permeability resonance. [...] Read more.

We revisit the standard Nicolson–Ross–Weir method of effective permittivity and permeability restoration of photonic structures for the case of subwavelength metal-dielectric multilayers. We show that the direct application of the standard method yields a false zero-epsilon point and an associated spurious permeability resonance. We show how this artifact can be worked around by the use of the cycle shift operator to the periodic multilayer in question. Full article

(This article belongs to the Special Issue Photonic Crystals)

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9780 KiB

Open AccessArticle

Hexaethylguanidinium Salts

by Robert Salchner, Volker Kahlenberg, Thomas Gelbrich, Klaus Wurst, Martin Rauch, Gerhard Laus and Herwig Schottenberger

Crystals 2014, 4(3), 404-416; https://doi.org/10.3390/cryst4030404 - 05 Sep 2014

Cited by 7 | Viewed by 5550

Abstract

Crystal structures of five hexaethylguanidinium salts (PF₆⁻ 1, FeCl₄⁻ 2, CuCl₄²⁻·H₂O 3, CoBr₄²⁻/Br⁻·H₂O 4, bistriflimide 5) were determined. Short interionic contacts were [...] Read more.

Crystal structures of five hexaethylguanidinium salts (PF₆⁻ 1, FeCl₄⁻ 2, CuCl₄²⁻·H₂O 3, CoBr₄²⁻/Br⁻·H₂O 4, bistriflimide 5) were determined. Short interionic contacts were identified. Cyclic voltammetry of 2 revealed an electrochemical window from +1.0 to −1.5 V with a single Fe(III)/Fe(II) redox event at −0.27 V on a gold electrode versus Ag/AgCl. Full article

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596 KiB

Open AccessArticle

Modeling the Shape of Ions in Pyrite-Type Crystals

by Mario Birkholz

Crystals 2014, 4(3), 390-403; https://doi.org/10.3390/cryst4030390 - 03 Sep 2014

Cited by 5 | Viewed by 16049

Abstract

The geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point [...] Read more.

The geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point groups, however, the ionic radius must be assumed to be an anisotropic quantity. An appropriate modelling of p valence ions then has to be performed by ellipsoids. The approach is tested for pyrite-structured dichalcogenides MX₂, with chalcogen ions X = O, S, Se and Te. The latter are found to exhibit the shape of ellipsoids being compressed along the <111> symmetry axes, with two radii r_|| and r_⊥ describing their spatial extension. Based on this ansatz, accurate interatomic M–X distances can be derived and a consistent geometrical model emerges for pyrite-structured compounds. Remarkably, the volumes of chalcogen ions are found to vary only little in different MX₂ compounds, suggesting the ionic volume rather than the ionic radius to behave as a crystal-chemical constant. Full article

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771 KiB

Open AccessArticle

Phase Energy Determined from Stress and Electric-Field-Induced Phase Transformations in [011]_C Cut 0.24PIN-PMN-PT Single Crystals

by Dorinamaria Carka, John A. Gallagher and Christopher S. Lynch

Crystals 2014, 4(3), 377-389; https://doi.org/10.3390/cryst4030377 - 19 Aug 2014

Cited by 5 | Viewed by 6252

Abstract

The effect of composition and temperature on the large field behavior of [011]_C cut and poled (d₃₂-mode) rhombohedral relaxor ferroelectric 0.24PIN-(1−x)PMN-xPT single crystals was characterized under electromechanical loading and the relative phase energy determined. The [...] Read more.

The effect of composition and temperature on the large field behavior of [011]_C cut and poled (d₃₂-mode) rhombohedral relaxor ferroelectric 0.24PIN-(1−x)PMN-xPT single crystals was characterized under electromechanical loading and the relative phase energy determined. The electric field and stress induced polarization and strain response and field dependent material properties are reported for two concentrations of lead titanate (PT), with one PT concentration closer to the morphotropic phase boundary, at low and high temperature. A thermodynamic analysis to determine the relative energy levels of the rhombohedral and orthorhombic phases is based on the path integration of the measured data to determine external work done to drive the phase transition. The effect of heat generated by irreversible strain and electric displacement increments (hysteresis in the phase transformation) was removed from the work done during the loading cycle and the relative Helmholtz free energy density levels of the phases was determined. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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2524 KiB

Open AccessReview

Relaxor-PT Single Crystal Piezoelectric Sensors

by Xiaoning Jiang, Jinwook Kim and Kyugrim Kim

Crystals 2014, 4(3), 351-376; https://doi.org/10.3390/cryst4030351 - 28 Jul 2014

Cited by 53 | Viewed by 12531

Abstract

Relaxor-PbTiO₃ piezoelectric single crystals have been widely used in a broad range of electromechanical devices, including piezoelectric sensors, actuators, and transducers. This paper reviews the unique properties of these single crystals for piezoelectric sensors. Design, fabrication and characterization of various relaxor-PT single [...] Read more.

Relaxor-PbTiO₃ piezoelectric single crystals have been widely used in a broad range of electromechanical devices, including piezoelectric sensors, actuators, and transducers. This paper reviews the unique properties of these single crystals for piezoelectric sensors. Design, fabrication and characterization of various relaxor-PT single crystal piezoelectric sensors and their applications are presented and compared with their piezoelectric ceramic counterparts. Newly applicable fields and future trends of relaxor-PT sensors are also suggested in this review paper. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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679 KiB

Open AccessArticle

High-Q Defect-Free 2D Photonic Crystal Cavity from Random Localised Disorder

by Kelvin Chung, Timothy J. Karle, Ranjith Rajasekharan, C. Martijn De Sterke and Snjezana Tomljenovic-Hanic

Crystals 2014, 4(3), 342-350; https://doi.org/10.3390/cryst4030342 - 16 Jul 2014

Cited by 1 | Viewed by 6952

Abstract

We propose a high-Q photonic crystal cavity formed by introducing random disorder to the central region of an otherwise defect-free photonic crystal slab (PhC). Three-dimensional finite-difference time-domain simulations determine the frequency, quality factor, Q, and modal volume, V, of the [...] Read more.

We propose a high-Q photonic crystal cavity formed by introducing random disorder to the central region of an otherwise defect-free photonic crystal slab (PhC). Three-dimensional finite-difference time-domain simulations determine the frequency, quality factor, Q, and modal volume, V, of the localized modes formed by the disorder. Relatively large Purcell factors of 500–800 are calculated for these cavities, which can be achieved for a large range of degrees of disorders. Full article

(This article belongs to the Special Issue Photonic Crystals)

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10872 KiB

Open AccessReview

Growth and Characterization on PMN-PT-Based Single Crystals

by Jian Tian and Pengdi Han

Crystals 2014, 4(3), 331-341; https://doi.org/10.3390/cryst4030331 - 16 Jul 2014

Cited by 11 | Viewed by 7948

Abstract

Lead magnesium niobate—lead titanate (PMN-PT) single crystals have been successfully commercialized in medical ultrasound imaging. The superior properties of PMN-PT crystals over the legacy piezoelectric ceramics lead zirconate titanate (PZT) enabled ultrasound transducers with enhanced imaging (broad bandwidth and improved sensitivity). To obtain [...] Read more.

Lead magnesium niobate—lead titanate (PMN-PT) single crystals have been successfully commercialized in medical ultrasound imaging. The superior properties of PMN-PT crystals over the legacy piezoelectric ceramics lead zirconate titanate (PZT) enabled ultrasound transducers with enhanced imaging (broad bandwidth and improved sensitivity). To obtain high quality and relatively low cost single crystals for commercial production, PMN-PT single crystals were grown with modified Bridgman method, by which crystals were grown directly from stoichiometric melt without flux. For ultrasound imaging application, [001] crystal growth is essential to provide uniform composition and property within a crystal plate, which is critical for transducer performance. In addition, improvement in crystal growth technique is under development with the goals of improving the composition homogeneity along crystal growth direction and reducing unit cost of crystals. In recent years, PIN-PMN-PT single crystals have been developed with higher de-poling temperature and coercive field to provide improved thermal and electrical stability for transducer application. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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3842 KiB

Open AccessReview

Advances in the Growth and Characterization of Relaxor-PT-Based Ferroelectric Single Crystals

by Jun Luo and Shujun Zhang

Crystals 2014, 4(3), 306-330; https://doi.org/10.3390/cryst4030306 - 16 Jul 2014

Cited by 46 | Viewed by 10227

Abstract

Compared to Pb(Zr_1−xTi_x)O₃ (PZT) polycrystalline ceramics, relaxor-PT single crystals offer significantly improved performance with extremely high electromechanical coupling and piezoelectric coefficients, making them promising materials for piezoelectric transducers, sensors and actuators. The recent advances in crystal growth [...] Read more.

Compared to Pb(Zr_1−xTi_x)O₃ (PZT) polycrystalline ceramics, relaxor-PT single crystals offer significantly improved performance with extremely high electromechanical coupling and piezoelectric coefficients, making them promising materials for piezoelectric transducers, sensors and actuators. The recent advances in crystal growth and characterization of relaxor-PT-based ferroelectric single crystals are reviewed in this paper with emphases on the following topics: (1) the large crystal growth of binary and ternary relaxor-PT-based ferroelectric crystals for commercialization; (2) the composition segregation in the crystals grown from such a solid-solution system and possible solutions to reduce it; (3) the crystal growth from new binary and ternary compositions to expand the operating temperature and electric field; (4) the crystallographic orientation dependence and anisotropic behaviors of relaxor-PT-based ferroelectriccrystals; and (5) the characterization of the dielectric, elastic and piezoelectric properties of the relaxor-PT-based ferroelectriccrystals under small and large electric fields. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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12884 KiB

Open AccessArticle

Preparation and Characterization of Lead-Free (K_0.5Na_0.5)NbO₃-LiNbO₃ and (K_0.5Na_0.5)NbO₃-LiTaO₃ Ferroelectric Single Crystals

by Tao Chu, Chao He, Hamel Tailor and Xifa Long

Crystals 2014, 4(3), 296-305; https://doi.org/10.3390/cryst4030296 - 16 Jul 2014

Cited by 4 | Viewed by 6304

Abstract

Lead-free (K_0.5Na_0.5)NbO₃-LiNbO₃(KNN-LN) and (K_0.5Na_0.5)NbO₃-LiTaO₃ (KNN-LT) ferroelectric single crystals, with the dimensions of 11 ´ 11 ´ 5 mm³ and 5 ´ 5 ´ 3 mm³, [...] Read more.

Lead-free (K_0.5Na_0.5)NbO₃-LiNbO₃(KNN-LN) and (K_0.5Na_0.5)NbO₃-LiTaO₃ (KNN-LT) ferroelectric single crystals, with the dimensions of 11 ´ 11 ´ 5 mm³ and 5 ´ 5 ´ 3 mm³, were grown successfully using the top-seeded solution growth (TSSG) method, respectively. The crystal structures were analyzed by means of X-ray diffraction, showing orthorhombic symmetry for KNN-LN single crystals and coexistence of orthorhombic and tetragonal symmetry for KNN-LT single crystals at room temperature. The orthorhombic-tetragonal (T_O-T) and tetragonal-cubic (T_C) phase transition temperatures are 195 °C and 420 °C for the KNN-LN single crystals, and 130 °C and 280 °C for KNN-LT single crystals, respectively. The remnant polarization (P_r) is 27.8 μC/cm² with a coercive ﬁeld (E_c) of 17 kV/cm for KNN-LT single crystals. The two single crystals showed 90° domains with layers in (parallel) straight lines, while KNN-LT single crystals have a larger domain region. The actual stoichiometry deviates easily from the original composition in the process of crystal growth, thus, an appropriate nominal composition and optimized crystal growth method is desired to get high-quality crystals in the future. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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4648 KiB

Open AccessReview

Polarization Rotation and Monoclinic Distortion in Ferroelectric (Bi_0.5Na_0.5)TiO₃–BaTiO₃ Single Crystals under Electric Fields

by Motohiro Ogino, Yuji Noguchi, Yuuki Kitanaka, Masaru Miyayama, Chikako Moriyoshi and Yoshihiro Kuroiwa

Crystals 2014, 4(3), 273-295; https://doi.org/10.3390/cryst4030273 - 16 Jul 2014

Cited by 24 | Viewed by 10859

Abstract

The features of the crystal structures and spontaneous polarization (P_s) under an electric field (E) have been reviewed for (1 − x)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃ (BNT–BT). In-situ measurements of high-resolution synchrotron [...] Read more.

The features of the crystal structures and spontaneous polarization (P_s) under an electric field (E) have been reviewed for (1 − x)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃ (BNT–BT). In-situ measurements of high-resolution synchrotron radiation X-ray diffraction (SR-XRD) under electric fields show that single crystals with x = 0 (BNT) and 5% have a monoclinic distortion in space group Cc at 25 °C. The SR-XRD study combined with density functional theory (DFT) calculations demonstrates that BNT–5%BT exhibits a rotation of P_s in the monoclinic a–c plane by 2° under an E of 70 kV/cm along the <001> pseudo-cubic direction, which is much larger than BNT. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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915 KiB

Open AccessArticle

Temperature-Dependent Phase Transition in Orthorhombic [011]_c Pb(Mg_1/3Nb_2/3) O₃-0.35PbTiO₃ Single Crystal

by Wenhui He, Qiang Li, Qingfeng Yan, Nengneng Luo, Yiling Zhang, Xiangcheng Chu and Dezhong Shen

Crystals 2014, 4(3), 262-272; https://doi.org/10.3390/cryst4030262 - 11 Jul 2014

Cited by 19 | Viewed by 9416

Abstract

Relaxor [011]_c PMN-0.35PT single crystal phase transition characteristics are investigated through various methods including variable temperature dielectric properties, X-ray diffraction, bipolar ferroelectric hysteresis loops (P-E) and electric-field-induced strain (S-E) hysteresis loops measurements. The results reveal that two phase transitions exist within the [...] Read more.

Relaxor [011]_c PMN-0.35PT single crystal phase transition characteristics are investigated through various methods including variable temperature dielectric properties, X-ray diffraction, bipolar ferroelectric hysteresis loops (P-E) and electric-field-induced strain (S-E) hysteresis loops measurements. The results reveal that two phase transitions exist within the range from room temperature to 250 °C: orthorhombic (O)-tetragonal (T)-cubic (C). The O-to-T and T-to-C phase transition temperatures have been identified as 84 °C and 152 °C, respectively. Diffuseness degree of the T-to-C phase transition for the unpoled single crystal has been calculated to be 1.56, implying an intermediate state between normal and relaxor ferroelectrics. Temperature-dependent remanent polarization (P_r), coercive field (E_c), saturation polarization (P_s), hysteresis loop squareness (R_sq), and longitudinal piezoelectric constant (d* 33) are also explored to learn the details of the phase transitions. Variable temperature unipolar S_uni-E hysteresis loops avail additional evidence for the microstructure change in the as-measured single crystal. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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1180 KiB

Open AccessReview

Rare-Earth Calcium Oxyborate Piezoelectric Crystals ReCa₄O(BO₃)₃: Growth and Piezoelectric Characterizations

by Fapeng Yu, Xiulan Duan, Shujun Zhang, Qingming Lu and Xian Zhao

Crystals 2014, 4(3), 241-261; https://doi.org/10.3390/cryst4030241 - 08 Jul 2014

Cited by 26 | Viewed by 10527

Abstract

Rare-earth calcium oxyborate crystals, ReCa₄O(BO₃)₃ (ReCOB, Re = Er, Y, Gd, Sm, Nd, Pr, and La ), are potential piezoelectric materials for ultrahigh temperature sensor applications, due to their high electrical resistivity at elevated temperature, high piezoelectric sensitivity [...] Read more.

Rare-earth calcium oxyborate crystals, ReCa₄O(BO₃)₃ (ReCOB, Re = Er, Y, Gd, Sm, Nd, Pr, and La ), are potential piezoelectric materials for ultrahigh temperature sensor applications, due to their high electrical resistivity at elevated temperature, high piezoelectric sensitivity and temperature stability. In this paper, different techniques for ReCOB single-crystal growth are introduced, including the Bridgman and Czochralski pulling methods. Crystal orientations and the relationships between the crystallographic and physical axes of the monoclinic ReCOB crystals are discussed. The procedures for dielectric, elastic, electromechanical and piezoelectric property characterization, taking advantage of the impedance method, are presented. In addition, the maximum piezoelectric coefficients for different piezoelectric vibration modes are explored, and the optimized crystal cuts free of piezoelectric cross-talk are obtained by rotation calculations. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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2237 KiB

Open AccessArticle

Quasi-Linear Polarized Modes in Y-Rotated Piezoelectric GaPO₄ Plates

by Cinzia Caliendo and Fabio Lo Castro

Crystals 2014, 4(3), 228-240; https://doi.org/10.3390/cryst4030228 - 07 Jul 2014

Cited by 6 | Viewed by 5569

Abstract

The propagation of both surface and flexural acoustic plate modes along y-rotated x-propagation GaPO₄ piezoelectric substrates was studied for several y-cut angles: the phase velocity and coupling coefficient dispersion curves were theoretically calculated for two different electroacoustic coupling configurations. [...] Read more.

The propagation of both surface and flexural acoustic plate modes along y-rotated x-propagation GaPO₄ piezoelectric substrates was studied for several y-cut angles: the phase velocity and coupling coefficient dispersion curves were theoretically calculated for two different electroacoustic coupling configurations. The investigation of the acoustic field profile across the plate thickness revealed the presence of thin plate modes having polarization predominantly oriented along the propagation direction, and hence suitable for operation in liquid environment. These modes include the linearly polarized Anisimkin Jr. and the quasi longitudinal plate modes, AMs and QLs, showing a phase velocity close to that of the longitudinal bulk acoustic wave propagating in the same direction. The temperature coefficient of delay (TCD) of these longitudinal modes was investigated in the −20 to 420 °C temperature range, in order to identify thermally stable or low TCD cuts. The power flow angle, i.e., the angle between the phase and group velocity vectors, was also estimated to evaluate the substrate anisotropy effect on the acoustic wave propagation. The GaPO₄ intrinsic properties, such as its resistance to high temperature and its chemical inertness, make it especially attractive for the development of acoustic waves-based sensors for applications in harsh liquid environment. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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686 KiB

Open AccessArticle

Combinatorial Frequency Generation in Quasi-Periodic Stacks of Nonlinear Dielectric Layers

by Oksana Shramkova and Alexander Schuchinsky

Crystals 2014, 4(3), 209-227; https://doi.org/10.3390/cryst4030209 - 01 Jul 2014

Cited by 2 | Viewed by 5273

Abstract

Three-wave mixing in quasi-periodic structures (QPSs) composed of nonlinear anisotropic dielectric layers, stacked in Fibonacci and Thue-Morse sequences, has been explored at illumination by a pair of pump waves with dissimilar frequencies and incidence angles. A new formulation of the nonlinear scattering problem [...] Read more.

Three-wave mixing in quasi-periodic structures (QPSs) composed of nonlinear anisotropic dielectric layers, stacked in Fibonacci and Thue-Morse sequences, has been explored at illumination by a pair of pump waves with dissimilar frequencies and incidence angles. A new formulation of the nonlinear scattering problem has enabled the QPS analysis as a perturbed periodic structure with defects. The obtained solutions have revealed the effects of stack composition and constituent layer parameters, including losses, on the properties of combinatorial frequency generation (CFG). The CFG features illustrated by the simulation results are discussed. It is demonstrated that quasi-periodic stacks can achieve a higher efficiency of CFG than regular periodic multilayers. Full article

(This article belongs to the Special Issue Photonic Crystals)

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3348 KiB

Open AccessReview

Potential Advantage of Multiple Alkali Metal Doped KNbO₃ Single Crystals

by Hideo Kimura, Hongyang Zhao, Rumi Tanahashi, Lei Guo, Tingting Jia, Qiwen Yao and Zhenxiang Cheng

Crystals 2014, 4(3), 190-208; https://doi.org/10.3390/cryst4030190 - 26 Jun 2014

Cited by 6 | Viewed by 6517

Abstract

Potassium niobate crystal KNbO₃ (KN) is a well-known crystal for lead free piezoelectric or nonlinear optical applications. The KN crystal has been studied in both single crystal form and in thin film form which has resulted in many review articles being published. [...] Read more.

Potassium niobate crystal KNbO₃ (KN) is a well-known crystal for lead free piezoelectric or nonlinear optical applications. The KN crystal has been studied in both single crystal form and in thin film form which has resulted in many review articles being published. In order to exceed the KN crystal, it is important to study KN phase forming and doping effects on the K site. This article summarizes the authors’ study towards a multiple alkali metal doped KN crystal and related single crystals briefly from the viewpoint of crystal growth. Full article

(This article belongs to the Special Issue Piezoelectric Crystals)

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Crystals, Volume 4, Issue 3 (September 2014) – 15 articles , Pages 190-426

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