Crystals

563 KiB

Open AccessReview

Flux-Grown Piezoelectric Materials: Application to α-Quartz Analogues

by Pascale Armand, Adrien Lignie, Marion Beaurain and Philippe Papet

Crystals 2014, 4(2), 168-189; https://doi.org/10.3390/cryst4020168 - 23 Jun 2014

Cited by 13 | Viewed by 8790

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 [...] 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 C_IJ (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 C^D₁₁ to C^E₁₁ 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)

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857 KiB

Open AccessArticle

Electric Field Effects on Photoluminescence of CdSe Nanoparticles in a PMMA Film

by Takakazu Nakabayashi, Ruriko Ohshima and Nobuhiro Ohta

Crystals 2014, 4(2), 152-167; https://doi.org/10.3390/cryst4020152 - 23 Jun 2014

Cited by 15 | Viewed by 6453

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 depends [...] 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)

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879 KiB

Open AccessArticle

Orientation and Temperature Dependence of Piezoelectric Properties for Sillenite-Type Bi₁₂TiO₂₀ and Bi₁₂SiO₂₀ Single Crystals

by Chuanying Shen, Huaijin Zhang, Yuanyuan Zhang, Honghao Xu, Haohai Yu, Jiyang Wang and Shujun Zhang

Crystals 2014, 4(2), 141-151; https://doi.org/10.3390/cryst4020141 - 20 Jun 2014

Cited by 17 | Viewed by 8308

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. In [...] 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)

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1043 KiB

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

by Kate Wittering, Josh King, Lynne H. Thomas and Chick C. Wilson

Crystals 2014, 4(2), 123-140; https://doi.org/10.3390/cryst4020123 - 11 Jun 2014

Cited by 13 | Viewed by 6484

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 bulk [...] 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)

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1765 KiB

Open AccessArticle

Tetragonal-to-Tetragonal Phase Transition in Lead-Free (K_xNa_1−x)NbO₃ (x = 0.11 and 0.17) Crystals

by Dabin Lin, Zhenrong Li, Fei Li, Changlong Cai, Weiguo Liu and Shujun Zhang

Crystals 2014, 4(2), 113-122; https://doi.org/10.3390/cryst4020113 - 10 Jun 2014

Cited by 9 | Viewed by 7852

Abstract

Lead free piezoelectric crystals of (K_xNa_1−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 [...] Read more.

Lead free piezoelectric crystals of (K_xNa_1−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 (K_xNa_1−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 (K_0.11Na_0.89)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)

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416 KiB

Open AccessCommunication

Structures and Magnetic Properties of Iron(III) Complexes with Long Alkyl Chains

by Manabu Nakaya, Kodai Shimayama, Kohei Takami, Kazuya Hirata, Saliu Alao Amolegbe, Masaaki Nakamura, Leonald F. Lindoy and Shinya Hayami

Crystals 2014, 4(2), 104-112; https://doi.org/10.3390/cryst4020104 - 15 May 2014

Cited by 7 | Viewed by 7269

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 compounds [...] 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)

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1109 KiB

Open AccessReview

Terahertz Vibrations and Hydrogen-Bonded Networks in Crystals

by Masae Takahashi

Crystals 2014, 4(2), 74-103; https://doi.org/10.3390/cryst4020074 - 31 Mar 2014

Cited by 73 | Viewed by 14270

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 noncovalent [...] 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)

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Crystals, Volume 4, Issue 2 (June 2014) – 7 articles , Pages 74-189

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