The intensity of the diffracted peak will depend on the shape of the crystallites because if you have needles or plates you will definitely have preferred orientations. In the case of powder X-ray diffraction we normally assume that the crystallites are randomly oriented. This will be the case only for specrically shaped crystallintes. You never have such spherically shaped crystallites in practice. Depending on the symmetry of the crystals and growth conditions one will normally have anisotropic shaped crystals and they will never pack with random orientations. So you will see some intensities stronger than expected whereas some will be weaker than expected from random orientation. But the total intensity diffracted should remain equal unless you have strong extinction or absorption effects. Rietveld refinement programs have the possibility for refining parameters for preferred orientations. This will introduce more parameters in the refinement but work well. One should try pulverize the sample before measurements such that the random orientation is minimum. Read standard books like X-ray Diffraction Procedures, Klud and Alexander.

The intensity of the diffracted peak will depend on the shape of the crystallites because if you have needles or plates you will definitely have preferred orientations. In the case of powder X-ray diffraction we normally assume that the crystallites are randomly oriented. This will be the case only for specrically shaped crystallintes. You never have such spherically shaped crystallites in practice. Depending on the symmetry of the crystals and growth conditions one will normally have anisotropic shaped crystals and they will never pack with random orientations. So you will see some intensities stronger than expected whereas some will be weaker than expected from random orientation. But the total intensity diffracted should remain equal unless you have strong extinction or absorption effects. Rietveld refinement programs have the possibility for refining parameters for preferred orientations. This will introduce more parameters in the refinement but work well. One should try pulverize the sample before measurements such that the random orientation is minimum. Read standard books like X-ray Diffraction Procedures, Klud and Alexander.

What is the material you are looking at? What is its space group? Do you know its structure? How do you make your sample? Do you know how to calculate the structure factor? You can then estimate the preferred orientation from the intensity you measure and the intensity you can calculate from the structure factor.

"Needle shape crystal are giving unusual large intensity in the powder pattern than the plate/block type crystals. Will the orientation of molecules make any difference in the intensity of the peaks??"

Of course it will! Go read virtually ANY fundamentals of XRD textbook for beginners, and look up orientation texture, effects of non-equiaxed powders on peak intensities, etc.

To add to Tapan's first answer, while it is correct as he states that "the total intensity diffracted should remain equal", it is in my experience unlikely that you will have adequate detector coverage in an ordinary x-ray diffractometer to see that equality.

There are several good references that provide strategies for sample preparation to reduce/minimize preferred orientation of powders (Klug and Alexander is an "oldie but goodie", and there are many others). Even so, with some samples a truly "random" orientation can be extraordinarily difficult to achieve.

In most cases, yes...

Consider u have anisotropic shape crystals. Example nanorod in c-axis. The crystal dimension in c direction is much larger than a or b directions, so (00l) peaks will be sharper, and the (h00), (0k0) and (hk0) will be broader. This will cause a preffered orientation. In some limit, the peaks even more higher than the others.

Example in March/Dollase model: if u had plate and needle-like shape in your sample, you can get the average percentage by input 2 same phases with different preffered orientation. But just refine the parameter not the direction.

Is there anyway to avoid this in PXRD profile. How to get the uniform PXRD peaks even though the crystals are even thin needle?

Try to grind the powder to get particle size < 5 or 1 micron, if u had direct ultrasonic it will further help reshape the particles.

Needle-like shape will always give u a preffered orientation if the ratio between the unique axis and the other r significant. But if u carefully load the powder to the sample holder without any treatment that can cause the particel to rearrange than maybe this will help.

Sudalai! "to get the uniform PXRD peaks even though the crystals are even thin needle" You would have to change the Nano structure of your sample as Michael Tem has suggested. The variations in XRD relative intensities of the 2D diffraction pattern can yield detailed Nano structural parameters non-destructively. What makes you want to throw all that valuable data away?

The simple answer to your original question is, absolutely! The intensity will certainly depend on the size/shape/orientation of the constituents. Please remember that each particle will create a spot when it satisfies the Bragg condition.

"Is there any relation between the morphology of micro/macrocrystalline and the intensity of its X-ray powder pattern?" Absolutely and unequivocally.

The challenge in most of your practical situations is the use of the ubiquitous 0D point/scintillation counter to acquire the 1D diffractogram instead of a 2D array detector and acquiring the 3D diffractogram. The conventional 1D diffractogram is "blind" to several Nano structural morphologies. Therefore difficult, complicated and sometimes impossible to analyze and extract such information. For instance, there is no way you could quantify the "preferred orientation" by just analyzing a single 1D equatorial diffractogram. (You'd be better off using the nearly extinct photographic dental film for this case). The shape and size of the reciprocal space volume is directly related to the Nano structural morphology of the sample.

The following LinkedIn discussion may be helpful to you:

"The 3rd Dimension and beyond in XRD 2013" by Weiguang Guan! How to use FREEWARE! August 21st 3D visualization of XRD - McMaster University. http://www.chemistry.mcmaster.ca/facilities/xray/221-max3d

http://www.linkedin.com/groupItem?view=&gid=2683600&type=member&item=264379262&qid=4c57cca1-128e-43ac-852f-d429b3025a71&trk=groups_most_popular-0-b-ttl&goback=%2Egmp_2683600

1. Intensity depends on the morphology of a sample. Normally you do not need intensities. What you need is a structure factor. Use proper LP factor to convert intensities to structure factor.

2. You can use something like vaseline to prepare a sample without preferred oritnetation. Put your powder into vaseline, mix it and enjoy.