Just like mitchellsimoens, I was able to use the external data provided just fine. However, I wasn't able to get the code to work with the return to bring up the chart. Instead, you might be looking to put the chart into a panel or window as it's item.

Also, I was not able to get the chart to work with the theme config. Once I took it out it worked just fine. Here's how I got it to work, and this may be what you're looking for.

app.js
Code:
var store = Ext.create('Ext.data.Store', {
    autoLoad: true,
    fields: ['name', 'data1'],
    
    proxy: {
        type: 'ajax',
        url: 'data.json',
        reader: {
            type: 'json'
        }
    }
});


var chart = {
    xtype: 'chart',
    store: store,
    width: 300,
    height: 500,
    animate: true,
    axes: [{
        type: 'Category',
        position: 'left',
        title: 'Places',
        fields: ['name']
    }, {
        type: 'Numeric',
        position: 'bottom',
        title: 'CTR',
        fields: ['data1'],
        grid: true,
        minimum: 0
    }],
    series: [{
        type: 'bar',
        axis: 'bottom',
        tips: {
            trackMouse: true, 
            width: 140, 
            height: 28,                
            renderer: function(storeItem) {
                this.setTitle(storeItem.get('data1') + ' data1')
            }
        },
        xField: 'name',
        yField: ['data1']
    }]
};

Ext.create('Ext.panel.Panel', {
    width: 300,
    height: 500,
    renderTo: Ext.getBody(),
    layout: 'fit',
    items: [chart]
});
data.json
Code:
[
    {"name": "banner_1", "data1": 0.15},
    {"name": "banner_2", "data1": 0.12}
]
Like this the chart can be called up in the item of windows, panels, etc pretty easily.
Hopefully this helps out.