Next Issue
Previous Issue

Table of Contents

Crystals, Volume 4, Issue 2 (June 2014), Pages 74-189

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-7
Export citation of selected articles as:

Research

Jump to: Review

Open AccessCommunication Structures and Magnetic Properties of Iron(III) Complexes with Long Alkyl Chains
Crystals 2014, 4(2), 104-112; doi:10.3390/cryst4020104
Received: 26 February 2014 / Revised: 3 April 2014 / Accepted: 7 May 2014 / Published: 15 May 2014
Cited by 1 | PDF Full-text (416 KB) | HTML Full-text | XML Full-text
Abstract
Iron(III) compounds with long alkyl chains, [Fe(Cn-pap)2]ClO4 (Cn-pap: alkoxy-2-(2-pyridylmethyleneamino)phenol, n = 8 (1), 10 (2), 12 (3), 14 (4), 16 (5)) have been synthesized. The [...] Read more.
Iron(III) compounds with long alkyl chains, [Fe(Cn-pap)2]ClO4 (Cn-pap: alkoxy-2-(2-pyridylmethyleneamino)phenol, n = 8 (1), 10 (2), 12 (3), 14 (4), 16 (5)) have been synthesized. The compounds were characterized by single crystal X-ray structure analysis and temperature dependent magnetic susceptibility in order to research the relationship between magnetic properties and the presence of long alkyl chains in soft molecules of the present type. The compounds 1, 2, 3 and 4 are in the high-spin (HS) state over the temperature range of 5 to 400 K. On the other hand, compound 5 is low-spin (LS) showing that the difference in magnetic properties depends on the length of the alkyl chain in the respective compounds. Full article
(This article belongs to the Special Issue Crystal Engineering Involving Weak Bonds)
Open AccessArticle Tetragonal-to-Tetragonal Phase Transition in Lead-Free (KxNa1−x)NbO3 (x = 0.11 and 0.17) Crystals
Crystals 2014, 4(2), 113-122; doi:10.3390/cryst4020113
Received: 13 April 2014 / Revised: 16 May 2014 / Accepted: 16 May 2014 / Published: 10 June 2014
PDF Full-text (1765 KB) | HTML Full-text | XML Full-text
Abstract
Lead free piezoelectric crystals of (KxNa1−x)NbO3 (x = 0.11 and 0.17) have been grown by the modified Bridgman method. The structure and chemical composition of the obtained crystals were determined by X-ray diffraction (XRD) and [...] Read more.
Lead free piezoelectric crystals of (KxNa1−x)NbO3 (x = 0.11 and 0.17) have been grown by the modified Bridgman method. The structure and chemical composition of the obtained crystals were determined by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The domain structure evolution with increasing temperature for (KxNa1−x)NbO3 (x = 0.11 and 0.17) crystals was observed using polarized light microscopy (PLM), where distinguished changes of the domain structures were found to occur at 400 °C and 412 °C respectively, corresponding to the tetragonal to tetragonal phase transition temperatures. Dielectric measurements performed on (K0.11Na0.89)NbO3 crystals exhibited tetragonal to tetragonal and tetragonal to cubic phase transitions temperatures at 405 °C and 496 °C, respectively. Full article
(This article belongs to the Special Issue Piezoelectric Crystals)
Open AccessArticle From Evaporative to Cooling Crystallisation: An Initial Co-Crystallisation Study of Cytosine and Its Fluorinated Derivative with 4-chloro-3,5-dinitrobenzoic Acid
Crystals 2014, 4(2), 123-140; doi:10.3390/cryst4020123
Received: 20 December 2013 / Revised: 21 May 2014 / Accepted: 29 May 2014 / Published: 11 June 2014
Cited by 2 | PDF Full-text (1043 KB) | HTML Full-text | XML Full-text
Abstract
Two new multi-component molecular complexes of cytosine and 5-fluorocytosine with 4-chloro-3,5-dinitrobenzoic acid are presented. Materials synthesis was achieved initially by evaporative crystallisation and the crystal structures determined. The process was then successfully transferred into a controlled small scale cooling crystallisation environment, with [...] Read more.
Two new multi-component molecular complexes of cytosine and 5-fluorocytosine with 4-chloro-3,5-dinitrobenzoic acid are presented. Materials synthesis was achieved initially by evaporative crystallisation and the crystal structures determined. The process was then successfully transferred into a controlled small scale cooling crystallisation environment, with bulk samples shown to be representative of the multi-component product phase, by powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) methods. Turbidity measurements are shown to be a valuable process analytical technology probe for characterising the initial stages of molecular complex formation in solution. The significance of these findings for scale-up of crystallisation of multi-component molecular materials and for future transfer into continuous cooling crystallisation is discussed. Full article
(This article belongs to the Special Issue Crystallisation Control)
Figures

Open AccessArticle Orientation and Temperature Dependence of Piezoelectric Properties for Sillenite-Type Bi12TiO20 and Bi12SiO20 Single Crystals
Crystals 2014, 4(2), 141-151; doi:10.3390/cryst4020141
Received: 30 April 2014 / Revised: 22 May 2014 / Accepted: 28 May 2014 / Published: 20 June 2014
PDF Full-text (879 KB) | HTML Full-text | XML Full-text
Abstract
The full matrix of electro-elastic constants of sillenite-type crystals Bi12TiO20 (BTO) and Bi12SiO20 (BSO) were determined by the resonance method, with d14 and k14 being on the order of 40–48 pC/N and 31%–36%, respectively. [...] Read more.
The full matrix of electro-elastic constants of sillenite-type crystals Bi12TiO20 (BTO) and Bi12SiO20 (BSO) were determined by the resonance method, with d14 and k14 being on the order of 40–48 pC/N and 31%–36%, respectively. In addition, double-rotated orientation dependence of d33 was investigated, with the maximum values of 25–28 pC/N being achieved in ZXtl45°/54°-cut samples. The electrical resistivity of BSO was found to be two orders higher than that of BTO, being on the order of 7 × 105 Ω cm at 500 °C. The temperature dependence of dielectric and piezoelectric properties were investigated. BSO exhibited a high thermal stability in the temperature range of 25–500 °C, while BTO showed a variation of ~3% in the range of 25–350 °C. The high values of d14 and k14, together with the good thermal stability, make BTO and BSO crystals potential candidates for electromechanical applications in medium temperature range. Full article
(This article belongs to the Special Issue Piezoelectric Crystals)
Figures

Open AccessArticle Electric Field Effects on Photoluminescence of CdSe Nanoparticles in a PMMA Film
Crystals 2014, 4(2), 152-167; doi:10.3390/cryst4020152
Received: 8 April 2014 / Revised: 4 June 2014 / Accepted: 6 June 2014 / Published: 23 June 2014
Cited by 2 | PDF Full-text (857 KB) | HTML Full-text | XML Full-text
Abstract
External electric field effects on spectra and decay of photoluminescence (PL) as well as on absorption spectra were measured for CdSe nanoparticles in a poly(methyl methacrylate) (PMMA) film. Electrophotoluminescence (E-PL) spectra as well as electroabsorption spectra show a remarkable Stark shift which [...] Read more.
External electric field effects on spectra and decay of photoluminescence (PL) as well as on absorption spectra were measured for CdSe nanoparticles in a poly(methyl methacrylate) (PMMA) film. Electrophotoluminescence (E-PL) spectra as well as electroabsorption spectra show a remarkable Stark shift which depends on the particle size, indicating a large electric dipole moment in the first exciton state. The E-PL spectra also show that PL of CdSe is quenched by application of electric fields, and the magnitude of the field-induced quenching becomes larger with increasing size. The PL decay profiles observed in the absence and presence of electric field show that the field-induced quenching of PL mainly originates from the field-induced decrease in population of the emitting state prepared through the relaxation from the photoexcited state. Full article
(This article belongs to the Special Issue Semiconductor Nanocrystals)
Figures

Review

Jump to: Research

Open AccessReview Terahertz Vibrations and Hydrogen-Bonded Networks in Crystals
Crystals 2014, 4(2), 74-103; doi:10.3390/cryst4020074
Received: 14 January 2014 / Revised: 3 March 2014 / Accepted: 4 March 2014 / Published: 31 March 2014
Cited by 4 | PDF Full-text (1109 KB) | HTML Full-text | XML Full-text
Abstract
The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz) spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating [...] Read more.
The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz) spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating noncovalent interactions has established the position of THz spectroscopy as a powerful tool for detecting the weak bonding in crystals. In this review, we are going to introduce, briefly, the contribution of weak bonds in the construction of molecular crystals first, and then, we will review THz spectroscopy as a powerful tool for detecting the formation of weak bonds and will show the significant contribution of advanced computational codes in treating noncovalent interactions. From the second section, following the Introduction, to the seventh section, before the conclusions, we describe: (1) the crystal packing forces, the hydrogen-bonded networks and their contribution to the construction of organic crystals; (2) the THz vibrations observed in hydrogen-bonded molecules; (3) the computational methods for analyzing the THz vibrations of hydrogen-bonded molecules; (4) the dispersion correction and anharmonicity incorporated into the first-principles calculations and their effect on the peak assignment of the THz spectrum (5) the temperature dependence; and (6) the polarization dependence of the THz spectrum. Full article
(This article belongs to the Special Issue Crystal Engineering Involving Weak Bonds)
Figures

Open AccessReview Flux-Grown Piezoelectric Materials: Application to α-Quartz Analogues
Crystals 2014, 4(2), 168-189; doi:10.3390/cryst4020168
Received: 22 April 2014 / Revised: 11 June 2014 / Accepted: 12 June 2014 / Published: 23 June 2014
Cited by 3 | PDF Full-text (563 KB) | HTML Full-text | XML Full-text
Abstract
Using the slow-cooling method in selected MoO3-based fluxes, single-crystals of GeO2 and GaPO4 materials with an α-quartz-like structure were grown at high temperatures (T ≥ 950 °C). These piezoelectric materials were obtained in millimeter-size as well-faceted, visually [...] Read more.
Using the slow-cooling method in selected MoO3-based fluxes, single-crystals of GeO2 and GaPO4 materials with an α-quartz-like structure were grown at high temperatures (T ≥ 950 °C). These piezoelectric materials were obtained in millimeter-size as well-faceted, visually colorless and transparent crystals. Compared to crystals grown by hydrothermal methods, infrared and Raman measurements revealed flux-grown samples without significant hydroxyl group contamination and thermal analyses demonstrated a total reversibility of the α-quartz ↔ β-cristobalite phase transition for GaPO4 and an absence of phase transition before melting for α-GeO2. The elastic constants CIJ (with I, J indices from 1 to 6) of these flux-grown piezoelectric crystals were experimentally determined at room and high temperatures. The ambient results for as-grown α-GaPO4 were in good agreement with those obtained from hydrothermally-grown samples and the two longitudinal elastic constants measured versus temperature up to 850 °C showed a monotonous evolution. The extraction of the ambient piezoelectric stress contribution e11 from the CD11 to CE11 difference gave for the piezoelectric strain coefficient d11 of flux-grown α-GeO2 crystal a value of 5.7(2) pC/N, which is more than twice that of α-quartz. As the α-quartz structure of GeO2 remained stable up to melting, a piezoelectric activity was observed up to 1000 °C. Full article
(This article belongs to the Special Issue Piezoelectric Crystals)

Journal Contact

MDPI AG
Crystals Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
crystals@mdpi.com
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Crystals
Back to Top