A review of β-Ga_2O_3 single crystal defects, their effects on device performance and their formation mechanism

As a wide-bandgap semiconductor(WBG), β-Ga_2O_3 is expected to be applied to power electronics and solar blind UV photodetectors. In this review, defects in β-Ga_2O_3 single crystals were summarized, including dislocations, voids, twin, and small defects. Their effects on device performance were discussed. Dislocations and their surrounding regions can act as paths for the leakage current of SBD in single crystals. However, not all voids lead to leakage current. There's no strong evidence yet to show small defects affect the electrical properties. Doping impurity was definitely irrelated to the leakage current. Finally, the formation mechanism of the defects was analyzed. Most small defects were induced by mechanical damages. The screw dislocation originated from a subgrain boundary. The edge dislocation lying on a plane slightly tilted towards the(102) plane, the(101) being the possible slip plane. The voids defects like hollow nanopipes, PNPs, NSGs and line-shaped grooves may be caused by the condensation of excess oxygen vacancies, penetration of tiny bubbles or local meltback. The nucleation of twin lamellae occurred at the initial stage of "shoulder part" during the crystal growth. These results are helpful in controlling the occurrence of crystal defects and improving the device performance.

Growth and fundamentals of bulk β-Ga_2O_3 single crystals

The rapid development of bulk β-Ga_2O_3 crystals has attracted much attention to their use as ultra-wide bandgap materials for next-generation power devices owing to its large bandgap(～ 4.9 eV) and large breakdown electric field of about8 MV/cm. Low cost and high quality of large β-Ga_2O_3 single-crystal substrates can be attained by melting growth techniques widely used in the industry. In this paper, we first present an overview of the properties of β-Ga_2O_3 crystals in bulk form. We then describe the various methods for producing bulk β-Ga_2O_3 crystals and their applications. Finally, we will present a future perspective of the research in the area in the area of single crystal growth.

Extraction and Crystal Structure of β-Sitosterol

The title compound β-sitosterol（C29H50O）, an active phytosterol in many medicinal and edible plants, was characterized by X-ray diffraction analysis and extensive nuclear magnetic resonance（NMR） data. It crystallizes in monoclinic system, space group P21 with C29H50O·1/2H2O, a = 9.4226（7）, b = 7.4824（9）, c = 36.889（3） , V = 2597.0（4） 3, Z = 4, Dx = 1.084 g/cm3, Mr = 423.70, F（000） = 948, and μ = 0.064 mm-1. The final R = 0.0886 and wR = 0.2234 for 10157 observed reflections（I 〉 2σ（I））. The molecular crystal structure of β-sitosterol shows relative stereochemistry of 24R-ethylcholest-5-en-3β-ol. The molecule is composed of one steroid nucleus（3 six-membered rings and 1 five-membered ring） and one sidechain of 10 carbons. There are two C29H50O molecules and one H2O molecule in a symmetrical unit, and the title compound is stacked into a special laminated structure through hydrogen bonds and van der Waal forces. The special laminated structure was first reported.

Synthesis,Crystal Structure and Catalytic Performance of the Trifluoro-substituted Mono(β-diiminato)Copper(Ⅱ)Complex

Two novel copper complexes with methyl or trifluoro-substituted mono-β-diiminato ligands and one acetoxyl anion were synthesized and characterized by IR spectroscopy and elemental analysis for the first time. The structure of complex 2 bearing trifluoro substituents was further confirmed by single-crystal X-ray diffraction. The crystal belongs to the triclinic system, space group P1 with a = 7.377（4）, b = 11.727（6）, c = 12.913（7） ？, α = 116.569（6）, β = 98.829（7）, γ = 96.520（6）°, V = 966.2（8） ？3, Z = 2, Mr = 479.86, Dc = 1.649 g/cm3, F（000） = 482, μ = 1.205 mm-1, the final R = 0.0370 and w R = 0.0903 for 3430 observed reflections with I 〉 2σ（I）. These mono-β-diiminato copper complexes can effectively catalyze methacrylate（MA） polymerization when activated by MMAO. The introduction of fluoro groups into the N-aryl ring of β-diiminato ligands can greatly increase the catalytic activity of copper complexes as well as the molecular weight of PMA.

Synthesis and Crystal Structure of α-( N-Protected a mino)β-lactam Derivative of 1 ,5-Benzothiazepine

The crystal of the title compound C, C 30 H 30 N 2O 3S has been prepared by reaction of 1,5 benzothiazepine with N protected glycine and determined by X ray single crystal diffraction. Crystal data: M r =498.62, triclinic with P 1 space group, a=10.880(2), b=13.955(3), c=9.537(2), α=99.34(3)°, β=110.43(3)°, γ=88 56(3)°, V=1338.2(5) 3, F(000)=528, λ (Mo Kα)=0.71073, Z=2, D c =1 237g/cm 3, μ =0.154mm -1 . Final R=0.0453, wR =0.1256 for 3491 observed reflections 〔 I>2σ(I) 〕. Structure analysis reveals that the substituents at C(23) and C(7) in four membered ring are located on the same side. The conformation of seven membered ring is chair like.

EFFECT OF N,N,N＇N＇-TETRAALKYL TEREPHTHALAMIDE ON NONISOTHERMAL CRYSTALLIZATION KINETICS OF POLYPROPYLENE

The effect of N,N,N＇,N＇-tetraalkyl terephthalamide （TATA） on the non-isothermal crystallization and melting characteristics ofpolypropylene （PP） was studied. The addition of TATA can lead to the formation ofβ-crystal PP. With the increase in TATA concentration the degree of crystallinity for β-crystal PP increased significantly, and that for a-crystal PP decreased, which indicated that TATA effectively induced the formation of β-crystal PP. WAXD also revealed the existence of β-crystal PP after the introduction of TATA into PP. PP containing TATA crystallized at a temperature range of 5-10℃ higher than that of pure PP, and the half-crystallization time （t1/2） and Avrami exponent （n） of PP at the same cooling rate were decreased by the addition of TATA, indicating that TATA influenced the crystallization rate and crystallization growth mode of PP. The rate constant of crystallization of PP containing TATA （Zc） was larger than that of pure PP, which further indicated that the crystallization of PP was accelerated by the addition of TATA.

Synthesis and Crystal Structure of (SiCl_3)_2Fe(CO)_4

The compound （SiCl3）2Fe（CO）4 was synthesized and structurally characterized by X-ray single-crystal diffraction. It crystallizes in monoclinic, space group P2 1/n with α = 8.287（2）, b = 9.829（2）, c = 9.042（2） A, β = 96.19（3）°, V= 732.2（3） A^3, C4Cl6FeO4Si2, Mr = 436.77, Z = 2, Dc = 1.981 g/cm^3, F（000） = 424, μ（MoKα） = 2.282 mm^-1, the final R = 0.048 and wR = 0.164 for 1109 observed reflections （I 〉 2σ（I））. The crystal structure of （SiCl3）2Fe（CO）4 reveals that the Si（l）- Fe-Si（l）^a sequence is linear and perpendicular to the Fe（CO）4 cross-shaped plane.

Synthesis and Crystal Structure of Bis(cyclopentadienyl) Ytterbium Complex Supported by β-Diketiminate

Treatment of the β-diketiminate-supported ytterbium dichloride LYbCl2（THF）2 1 （L = N,N＇-bis（2,6-dimethylphenyl）-2,4-pentanediiminate） with 2 equiv of C5H5Na gave rise to the title complex LYb（C5H5）2 2 （C31H35N2Yb, Mr = 608.65）, and its crystal structure was determined by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P2 1/n with a = 14.417（2）, b = 10.432（2）, c = 18.040（4） ,A°, β= 95.73（2）°, V= 2699.6（9） ,A°, Dc = 1.498 g/cm^3, Z = 4, 2（MoKa） = 0.71073 ,A°,μ = 3.485 mm^-1, F（000） = 1220, the final R = 0.0304 and wR = 0.0703 for 3962 observed reflections with I 〉 2σ（I）. In the molecular structure of the title complex, the central metal atom Yb is eight-coordinated by two cyclopentadienyl groups and two nitrogen atoms of ,β- diketiminate group to form a distorted tetrahedral geometry.

Synthesis, Crystal Structure and Antitumor Activities of 2-Acyl-β-lactam-2-carboxamides

A series of 2-acyl-β-lactam-2-carboxamides was prepared through a tandem Ugi 4 CC/SN cyclization of bromoacetic acid, primary amine, arylglyoxal, and isocyanide. All of them were characterized by NMR, IR, MS and elemental analysis. Meanwhile, the single crystal of compound 5 a, C_(19)H_(25)ClN_2 O_3, was also obtained and determined by X-ray crystallography. Crystal data: triclinic system, space group P_1, a = 8.1318(15), b = 11.931(2), c = 12.027(2) ?, α = 67.361(3)°, β = 73.009(3)°, γ = 85.663(3)°, V = 1029.1(3) ?3, Z = 2, F(000) = 388, Dc = 1.178 g/cm3, μ = 0.204 mm^(-1), R = 0.0786 and w R = 0.2212 for 3585 independent reflections(Rint = 0.0214) and 2960 observed ones(I > 2σ(I)). Intermolecular N–H···O stacking interactions contributed to the stability of the structure. The antitumor abilities of 5 were analyzed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazo-liumbromide(MTT) standard method; 5 c stood out as the most potent showing an IC_(50) of 1.70 μmol/L against human tumor cell lines(HepG2).

MULTIPLE MELTING BEHAVIOR OF β-CRYSTALLINE PHASE POLYPROPYLENE

Differential scanning calorimetry and X-ray diffraction experiments on β-nucleated polypropylene were made on the samples crystallized at different temperatures and processed by injection molding. The crystal perfection was shown to vary with crystallization temperature. The observed multiple peaks could be related to a ill-phase with defective inclination of the chains, a recrystallized or original β_2-phase of more perfect inclination, and the α-phase. Injection molded samples could be analyzed from the established DSC interpretation.

Synthesis and Crystal Structure of (3R,4R)-5-(2,4-Dichlorobenzoyl)-4-(4-nitrophenyl)-6-(phenylamino)-3,4-dihydro-2H-thiopyran-3-carbonitrile

The title compound（C25H16Cl2N3O3S）,as a thiopyran derivative,has been synthe-sized by the cyclization of an organic intermediate obtained from Baylis-Hillman adducts with a β-aroylthioamide using copper（I） salt as the catalyst.The crystal belongs to the monoclinic system,space group P21/c with a = 13.668（3）,b = 8.4803（17） c = 21.999（4） ,β = 113.57（3）°,V = 2337.2（10） 3,Z = 4,Mr = 510.38,Dc = 1.451 g/cm3,μ = 0.401 mm-1,F（000） = 1048,the final R = 0.0487 and wR = 0.1079 for 3678 observed reflections with I〉 2σ（I）.

Crystal Structure of 1-Phenyl-1,3-butandione Benzidine Diketoimine

1-Phenyl-1,3-butandione benzidine diketoimine 2a （C32H28N2O2, Mr = 472.56） was synthesized in high yield by the reaction of 1-phenyl-1,3-butandione with benzidine in absolute ethanol, and determined by X-ray structure analysis. It crystallizes in the orthorhombic system, space group P21/c with a = 7.9839（16）, b = 12.910（3）, c = 12.358（3）A, α = 90.00, β= 93.71（3）,γ = 90.00°, V = 1271.1（4） A3, Z = 2, Dc = 1.235 g/cm^3,/1 = 0.077 mm^-1, F（000） = 500, the final R = 0.0717 and wR = 0.1187. It presents a linear centrosymmetric framework constituted by a linkage of benzidine as a bridge and two terminal 1-phenyl-1,3-butanedione moieties.

Crystallization Behavior of Polymer Derived Silicon Carbide Sintered Through Microwave Heating Technique

A self-crosslinkable liquid highly branched polycarbosilane（LHBPCS） with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.

聚偏氟乙烯流延膜的制备与性能

含β晶体的聚偏氟乙烯(PVDF)的极性较强,是一种重要的压电和铁电材料,受到人们的广泛关注。在该工作中,选择了PVDF的3种β晶体成核剂,首先用傅里叶红外光谱(FTIR)比较了3种成核剂对PVDF流延膜中β晶体含量的影响,随后选择成核效率最高的成核剂四苯基溴化膦(TPPB),通过调整流延工艺制备了高β晶体含量的PVDF流延膜,最后利用广角X射线衍射(WAXS)及小角X射线散射(SAXS)技术研究了PVDF流延膜以及其在后拉伸过程中的结晶结构,同时研究了流延膜的力学性能以及弹性回复性能等。研究结果表明,PVDF/TPPB流延膜的β晶体含量和片晶取向程度随着流延膜牵伸比的增加而增大。随着牵伸比的增加,PVDF/TPPB流延膜的屈服应力和杨氏模量增大,弹性回复能力增强。同时,在流延膜的后拉伸过程中,随着拉伸应变的增加,流延膜出现空洞结构,并且温度越低,空洞出现的临界应变越小,这对含β晶体PVDF微孔膜的制备具有指导意义。

Crystal Structure of (E,E)-1,10-Bis-(4-fluoro-phenyl)-3,8-dimethyl-deca-3,7-diene-1,10-dione

The crystal and molecular structures of (E,E)-1,10-bis-(4-fluorophenyl)-3,8-dime- thyl-deca-3,7-diene-1,10-dione have been determined by X-ray diffraction method. The crystal (C24- H24F2O2, Mr = 382.45) is of monoclinic, space group P21/c, a = 11.0392(5), b = 11.3620(4), c = 7.9361(3) ?, β = 97.423(2)o, V = 987.06(7) ?3, Z = 2, Dc = 1.287 g/cm3, μ(Mo-Kα) = 0.93 cm-1, λ = 0.7107 ?, F(000) = 404.00, the final R = 0.0530 and wR = 0.150 for 1348 observed reflections (I > 2σ(I)). X-ray analysis revealed that there exists a double bond in C(9)–C(11) with the bond length of 1.324(3) ?, while the C(8)–C(9) bond length is 1.508(3) ? and it may be assigned to a single bond. These results show that the C=C bond is not conjugated with the C=O bond.

Synthesis and Crystal Structure of 3,6-Bis(4,4,4-trifluorobutane-1,3-dione)-9-n-butylcarbazole

A novel bis（β-diketonate） derivate, 3,6-bis（4,4,4-trifluorobutane-1,3-dione）-9-n- butylcarbazole 1, was synthesized and structurally characterized by single-crystal X-ray diffrac- tion. The crystal belongs to the monoclinic system, space group P2 1/c with a = 10.961（6）, b = 22.942（13）, c = 9.408（6）A, α = 90, β = 109.663（9）, y = 90°, V = 2228（2）A^3, Z = 4, Dc = 1.489 g/cm^3, C24H19F6NO4, Mr = 499.40, F（000） = 1024 and μ = 0.134 mm^-1. The structure was refined to the final R = 0.0699 and wR = 0.1627 for 3744 independent reflections （Rint = 0.1288） and 1349 observed reflections （I 〉 2σ（I））. Compound 1 consists of carbazole unit and two terminal diketonate groups, in which carbazole and its two adjacent diketonate rings are almost coplanar. Moreover, compound 1 was characterized with IR, elemental analysis, IH NMR, MS, electronic absorption, and single-photon fluorescence.

Synthesis and Crystal Structure of O-Ethyl-N- (2,3,4-tri-O-acetyl-β-D-xylopyranosyl)-thiocarbamate

The crystal and molecular structures of O-ethyl-N-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)-thiocarbamate were determined by X-ray crystallography. It crystallizes in the orthorhombic system with space group P2(1)2(1)2(1), lattice parameters a=0.90636(18) nm, b=0.94716(19) nm, c=2.1855(4) nm, V=1.8762(7) nm 3, and Z=4. All the substituents are in equatorial positions. There are four intramolecular interactions, each forming a five-membered ring. The molecules are linked by interactions to form three-dimensional framework. Atoms O6 and O8 show positional disorder.

SYNTHESIS AND MESOMORPHIC PROPERTIES OF PALLADIUM CHELATES OF LIQUID CRYSTAL POLYSILOXANE WITH β-DIKETONE-BASED SIDE CHAINS

A new type of palladium chelate of β-diketone-based side chain liquid crystal polysiloxane (Pd-DKLCP) has been synthesized by chelation reaction of palladium dichloride with polymeric ligand, β-diketone polysiloxane (DKLCP), using THF as solvent at R.T.. The Pd-chelation results in greatly increasing the phase transition temperature T_K and the enthalpy change △H_K from crystal to liquid crystal state and making the temperature range of LC state △T(△T=T_(Cl)-T_K) widened. All these chelates Pd-DKLCP's do not show T_(Cl) until decomposition at 205℃. It is noteworthy that the Pd-chelation can exert more positive effect on the mesomorphic behaviour of the polymer ligand than the counterpart Cu-DKLCP does. It is probable due to the bigger size of disc-like mesogen formed from β-diketone and Pd^(+2) ion with 4d orbital.

SYNTHESIS AND CHARACTERIZATION OF β-DIKETONE BASED SIDE CHAIN LIQUID CRYSTALLINE POLYSILOXANES

A new type of β-diketone based side chain liquid crystalline polysiloxanes (DKLCP) with different length of flexible spacers and end groups have been synthesized by hydrosilation reaction. This is liquid crystal polymers (LCP) using coordinating β-diketone ligand as mesogens. The phase behaviour of DKLCP polymers was studied by differential scanning calorimetry and polarizing microscopy. X-ray diffraction investigations demonstrated that the polysiloxanes with sufficiently long flexible spacers were smectic liquid crystal polymers, while those with much shorter spacers were nematic ones.

Synthesis, Crystal Structure and Characterization of a One-dimensional Supramolecular Rare Earth Complex of N-(6-(4-Methylpyridinyl))ketoacetamide

A one-dimensional （1D） supramolecular rare earth complex [Nd（NO3）2L2-（C3H6O）][NdL（NO3）4]} （L=N-（6-（4-methylpyridinyl））ketoacetamide） has been prepared and characterized by elemental analysis, IR and electronic spectroscopy, and single-crystal X-ray diffraction. The crystal crystallizes in the triclinic system, space group P1^- with a=0.9146（6）, b=1.2581（8）, c=2.2316（14） nm, α=99.352（10）,β=97.209（9）, γ=103.935（9）°, V=2.422（3） nm3, Dc=1.776 g/cm^3, C33H42N12Nd2O25, Mr=1295.27, Z=2, F（000）=1288, μ=2.217 mm-1, R=0.0508and wR=0.1046 for 5173 observed reflections （I 〉 2σ（I））. In the structure of the title complex,one-dimensional supramolecular double-chains are formed by intermolecular hydrogen bonding interactions.