Effect of Calcinations Temperature on Crystallography and Nanoparticles in ZnO Disk

We proposed a good calcinations condition of the ZnO disk to control the crystallography and nanoparticles in ZnO disk. The crystallography of precursor powder and disk powder were analyzed by the X-ray diffraction (XRD). The mean nanoparticles of ZnO disk was determinate by XRD results and observed by scanning electron microscope. The temperature ranges of 400 ̊C to 650 ̊C in air for 30 minutes were used calcinations ZnO disk. These temperature can be controlled the single phase, lattice parameters, unit cell volume, crystalline size, d-value, texture coefficient and bond lengths of Zn–Zn, Zn–O and O–O which correspond significantly the hexagonal crystal structure. The nanoparticles were small changed mean of 76.59 nm at the calcinations temperature range.


Introduction
Zinc oxide nanomaterials are interesting and have been developed in recent years because of their physical and chemical properties, which promote an achievement of high performance materials for various applications.Recently, many studies have been made in order to understand the microstructure, electrical properties and thermoelectric properties of ZnO for application.For examples, the varistor ceramics [1], luminescent materials [2], new coplanar gas sensor array [3], application of sunscreen nanoparticles [4] and, finally, impure ZnO materials are of great interest for high temperature thermoelectric application [5].
In this work, we report an analysis the effect of calcinations temperature on phase identification, lattice parameters, crystal structure, orientation, texture coefficient, bond length of Zn-Zn, Zn-O and O-O, powder distribution and powder size in ZnO disk for control the nanopowder in ZnO disk or tendency apply the ZnO disk to thermoelectric material.

Experimental
The ZnO precursor of nanopowder was synthesized by direct precipitation method using Zn(NO 3 ) 2 ฺ •6H 2 O (QRëC TM , 98.5% purity), (NH 4 ) 2 CO 3 (QRëC TM , 99.5% purity), ethanol, and de-ionized water.Firstly, Zn(NO 3 ) 2 ฺ •6H 2 O and (NH 4 ) 2 CO 3 were dissolved in de-ionized water by the vigorously stirring to form solutions with 1.5 and 2.25 mol/L concentrations, respectively.Secondly, the precipitates obtained by the reaction between the Zn(NO 3 ) 2 and the (NH 4 ) 2 CO 3 solutions were collected by filtration and rinsed three times with de-ionized water and ethanol, respectively, then washed and dried at 80˚C to form the precursor of nanopowder.The calcinations temperature was investigated by the relationship between the weight loss and temperature by using thermal gravimetric analysis (TGA-DTA/DSC; NETZSCH STA 449C).Finally, the precursor of nanopowder was pressured by the hydraulic press about 160 MPa in air to obtain the ZnO disk.The disk was calcinated at temperature range 400˚C to 650˚C in air for 30 minutes.The crystallography of precursor of powder and disk powder were analyzed by X-ray diffraction (XRD; PW1710) with a Cu-K1( = 0.15406 nm) source at 40 kV and 30 mA.The morphology of the precursor of powder and disk powder were observed by a scanning electron microscope (SEM; JSM-6100).The particle size (D) of precursor and disk powder were calculated by the Debye-Scherrer formula using raw data from XRD patterns and evaluated from SEM images.The crystalline size was calculated by the Debye-Scherrer formula as follows.
where is the crystalline size (in nm), D  is the wavelength (in nm),  is the full width at half maximum (FWHM-in radian) intensity, and  is the Bragg diffraction angle [6].The relative percentage error for all the disks was evaluated by the Equation ( 2) and JCPDS standard d-values [7].
Relative percentage error 100 where H Z is the actual obtained d-value in XRD patterns and Z is the standard d-value in JCPDS data.The particular plane and information were concerned by the preferential crystallite orientation determined from the texture coefficient [8] as follows: where the parameter is defined by u a and b are lattice parameters [11].The unit cell structure was designed by discrete variational X  method for evaluating Zn-O bond length [12].The volume of hexagonal primitive cell is and Brillouin zone is where is the volume of a crystal primitive cell [13].

Results and Discussion
The TGA curve shows a weight loss step at incremented temperatures from 25˚C to 1000˚C as shown in Therefore, we should the temperature range of 400˚C to 700˚C for calcinations the ZnO disk to control the nanoparticles.However, the disk has agglomerated powder and cracked at 700˚C.
The XRD patterns of the disk powder were calcinated at temperatures of 400˚C, 450˚C, 500˚C, 550˚C, 600˚C and 650˚C in air for 30 minutes are shown in Figure 2(a The values of c a and unit cell volume were corresponded to literature data [14][15][16][17] as shown in Figure 4. The full widths at half maxima (FWHM) of the (100), (002) and (101) index planes of 0.256, 0.256 and 0.26 nm, respectively, were uses for particle size calculation.The d-values, d% error and texture coefficient calculated by using Equation ( 2) and ( 3) are shown in Table 1.
The texture coefficient (TC (h k l)) values were calculated by Equation ( 3  to Equation (2), we know that the (1 0 0), (0 0 2) and (1 0 1) planes were the preferential crystallite orientation for the nanopowder of ZnO fabricated in this work.The TC (h k l) represents the texture of a particular plane, whose deviation from unity implies the preferred growth [18].It   2, where the Zn-O bond length is 1.9767 Å in the unit cell of ZnO and neighboring atoms.Viewing direction is approximately parallel to O 2− and Zn 2+ corresponding to literature data [20] and have a good thermoelectric power about −279 µV/K at 500˚C [21] which is close to the proposed calcinations temperature range.
The SEM images of nanopowder in ZnO disk after calcinations temperature of 400˚C, 450˚C, 500˚C, 550˚C, 600˚C and 650˚C, respectively are shown in Figure 5(a)-5(f).
The nanopowder of ZnO was exhibited a good distribution after being calcinated below 550˚C.The powder of ZnO was covered with nanopowder, while other portions retained the smooth morphology.The particle sizes were small increased from 73.50 to 79.67 nm with increasing calcinations temperature as shown in Figure 6.However, the nanopowder was agglomerated to form larger particle sizes at the calcinations temperature higher than 650˚C and disk fractured at 700˚C.

Conclusions
The temperature range of 400˚C to 650˚C was chosen for calcinations temperature and controled the nanoparticle in ZnO disk.The crystallography of disk powder was corresponding to the hexagonal structure and the lattice constants.The experimental d-values were in a good agreement with JCPDS I and indicated the hexagonal structure.The Zn-O bond length of 1.9767 Å was related with ZnO unit cell viewed direction approximate parallel to O 2− and Zn 2+ .The disk powder was exhibited good distribution after being calcinated below 550˚C covering with the nanoparticles, while other portions retained the smooth morphology and the mean particle size of 76.59.
is the standard intensity of the plane taking from the JCPDS data[9,10].The Zn-O bond length is given by

Figure 1 .Figure 1 .
Figure 1.TGA-DTA traces at a heating rate of 10˚C/min for ZnO precursor of powder.range 435˚C to 500˚C indicating that decomposition does not occur above this temperature and the stable nanoparticles.The XRD patterns of the precursor of powder were corresponded the patterns of JCPDS Card No.891397.The precursor of powder has been the lattice parameters a = b = 3.2481 Å, c = 5.2049 Å indicate hexagonal structure.Therefore, we should the temperature range of 400˚C to 700˚C for calcinations the ZnO disk to control the nanoparticles.However, the disk has agglomerated powder and cracked at 700˚C.The XRD patterns of the disk powder were calcinated at temperatures of 400˚C, 450˚C, 500˚C, 550˚C, 600˚C and 650˚C in air for 30 minutes are shown in Figure2(a)-2(f), respectively.The main peaks correspond to the hexagonal structure ZnO and the lattice constants a = b = 3.2469 Å increase to 3.2488 Å and c = 5.2049 Å slightly decrease to 5.2031 Å as shown in Figure 3.The values of c a and unit cell volume were corresponded to literature data[14][15][16][17] as shown in Figure4.The full widths at half maxima (FWHM) of the (100), (002) and (101) index planes of 0.256, 0.256 and 0.26 nm, respectively, were uses for particle size calculation.The d-values, d% error and texture coefficient calculated by using Equation (2) and (3) are shown in Table1.The average relative percentage errors of calcinations temperatures of 400˚C, 450˚C, 500˚C, 550˚C, 600˚C and 650˚C are 0.17%, 0.77%, 0.28%, 0.18%, 0.59%, and 0.29%, respectively.The experimental d-values and JCPDS d-values are in a good agreement and indicate hexagonal structure[9].The texture coefficient (TC (h k l)) values were calculated by Equation (3) and obtain a mean value of 0.35.The value TC (h k l) = 1 represents randomly oriented crystallites, while higher values indicate the abundance of grains oriented in a given (h k l) direction.According

)- 2 (
f), respectively.The main peaks correspond to the hexagonal structure ZnO and the lattice constants a = b = 3.2469 Å increase to 3.2488 Å and c = 5.2049 Å slightly decrease to 5.2031 Å as shown in Figure 3.

Figure 3 .
Figure 3.The calcinations temperature dependence on the lattice constants, a and c.

Figure 4 .
Figure 4.The calcinations temperature dependence on the ratio of c/a lattice constants and unit cell volume.

Table 2 . The bond length lists of ZnO compound.
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