Usually, crystallite size increases as peak intensity increases, meaning narrowing of peak width with increasing temperature. I observed the opposite where, I grew my samples at 1000 degree celsius but at varying gas flow rates. Crystallite size was observed to decrease with increasing peak intensity. What may be responsible for this behavour?
First, let's start with the meaning of "peak intensity". If one thinks that the maximum number of counts is the answer, he/she is wrong. The intensity of a peak is the total number of counts from left tail to right tail of the slopes of the peak. In other words, this is the area under the peak. It is called the "integral intensity". This value primarily depends on the amount of a phase in the sample, and also on the texture (if any) of the sample, and of course on relative intensity of peaks in a standard diffraction pattern.
The same integral intensity may be obtained for high and narrow peak, and for low and diffuse (wide) peak. Narrow peaks are obtained for coarse-grained samples. Wide peaks are obtained for very fine grains. Let's assume that you have 2 samples with the same amount of the considered phase, and texture is the same or the sample in not textured. This means that the considered peak will have the same integral intensity. One sample is obtained in conditions that provoke grain growth, and the other is obtained in conditions that reduce grain size. So, the coarse grained sample will exhibit narrow peak, and the fine grained will exhibit wide peak. If the area under both peaks is the same, then - naturally - the (maximum) height of coarse grained sample must be larger, and the (maximum) height of the fine grained sample must be smaller. As you see, there is nothing wrong with your results. Coarse grains give high and narrow peaks, and fine grains give low and wide peaks.
All these considerations were made with assumption that all other parameters of your samples are invariable. If they are not, the analysis of other factors influencing the XRD results must be included.
Dear Sir
The crystallite size is not the only parameter affecting the peak shape (width, height and position). The amount of phase, grain size, texture and… are also effective on peak shape. I think you should consider the effect of these parameters.
Yes, I also agree with the A. Shabani. Only peak intensity or peak width is not responsible for particle size but some other parameters are also effected. The intensity of the peak in a powder diffraction pattern is related to the volume (i.e. number of atoms), which is indirectly related to the particle size. An analytical formula was provided by Warren (1978) for spherical domains (it can be easily generalised to any shape). If we the volume is fixed, the intensity is preserved. If the volume is changed, then of course the intensity will changes. The relative intensity of the peak is related to the structure. Similarly, the structure, phases, texture and some other parameters are also responsible for peak width.
First, let's start with the meaning of "peak intensity". If one thinks that the maximum number of counts is the answer, he/she is wrong. The intensity of a peak is the total number of counts from left tail to right tail of the slopes of the peak. In other words, this is the area under the peak. It is called the "integral intensity". This value primarily depends on the amount of a phase in the sample, and also on the texture (if any) of the sample, and of course on relative intensity of peaks in a standard diffraction pattern.
The same integral intensity may be obtained for high and narrow peak, and for low and diffuse (wide) peak. Narrow peaks are obtained for coarse-grained samples. Wide peaks are obtained for very fine grains. Let's assume that you have 2 samples with the same amount of the considered phase, and texture is the same or the sample in not textured. This means that the considered peak will have the same integral intensity. One sample is obtained in conditions that provoke grain growth, and the other is obtained in conditions that reduce grain size. So, the coarse grained sample will exhibit narrow peak, and the fine grained will exhibit wide peak. If the area under both peaks is the same, then - naturally - the (maximum) height of coarse grained sample must be larger, and the (maximum) height of the fine grained sample must be smaller. As you see, there is nothing wrong with your results. Coarse grains give high and narrow peaks, and fine grains give low and wide peaks.
All these considerations were made with assumption that all other parameters of your samples are invariable. If they are not, the analysis of other factors influencing the XRD results must be included.
Several good answers that mention texture. I'd like to emphasize that preferred orientation can certainly change or become more pronounced with grain growth.
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